SC TIPS & TRICKS

A MAJOR EXCEPTION TO THE TOUCH RULE:
an essential modifier can separate "which" and its noun referent

Excellent questions! Yes, except for an unimportant phrase that I think is unidiomatic, the sentence is grammatically correct.

I changed the sentence slightly (see below), but the underlying concept remains the same.
You have created a sentence that is an exception to the "modifier touch rule."

• the "Touch Rule" for noun modifiers

The "touch rule" for noun modifiers states that the modifier of a noun should be as close as possible to the noun it modifies.
Some noun modifiers are essential (restrictive, vital)—we need these modifiers to establish the identity of the noun.
Some noun modifiers are nonessential (nonrestrictive, not vital). These modifiers give us some extra information but are not necessary to establish the identity of the noun.

The word "which" is a nonessential modifier.
On the GMAT and in formal writing in the U.S., the word "which" is preceded by a comma, this way: [comma + which clause]
If [comma + which] is placed in the middle of the sentence, the clause is set off by two commas, one at the beginning and one at the end.
If [comma + which] is placed at the end of the sentence, the clause is set off by only one comma: the one before the word which.

By contrast, the word that is an essential modifier that is not set off by commas.
(The distinction seems to be alive and well. This OG 2020 question, here tests the difference between that and which.
The house that the FBI raided is one block east of here. (The clause that the FBI raided is essential. Which house? The one that the FBI raided.)
The house that I grew up in, which new owners remodeled, is one block east of here. The phrase which new owners remodeled is not necessary to establish the identity of the house.

In a way similar to the word "that," prepositional phrases that modify a noun (noun + preposition + object of preposition) are essential modifiers (or cannot be placed elsewhere because of the structure of an English sentence).
-- Please do not topple this house of cards that took me an hour to build.
Remove "of cards." Now the noun is not the same: a house and a house of cards are different. The sentence makes no sense. I cannot build a real house in an hour any more than a person could "topple" such a house.

• A major exception to the Modifier Touch Rule: which can "reach back over" essential modifiers such as prepositional phrases in order to "reach" its noun

The word which is a nonessential modifier. Still, it should be as close to its noun as possible.
But if a sentence contains an essential noun modifier and a (nonessential) which-clause noun modifier, the which-clause is still allowed to modify its noun.
The word "which" can "reach back" over other essential modifiers in order to modify its noun.

That is, sometimes an essential or vital or restrictive modifier prevents the nonessential modifier from directly touching the noun.
Both the essential and non-essential modifiers refer to the same noun.
We cannot place both modifiers right next to the noun.
The essential modifier trumps (is more important than) the nonessential modifier and thus is placed right next to the noun.
The nonessential modifier which is placed right after the essential modifier and is allowed to "reach back" over that essential modifier in order to modify its noun.

• THE EXAMPLE SENTENCES, SLIGHTLY REWRITTEN. BOTH SENTENCES ARE CORRECT

I can write a book about how different people use the word “tomorrow” in each context, which if published will become a best-seller.
OR
I can write a book about how different people use the word “tomorrow” in each context, which, if published, will become a best-seller.*

Let's break them down
Subject: book
Essential modifier: "about how different people use the word “tomorrow” in each context"
WHICH refers to: book
Words that follow which: if published
The which-clause is not essential and is not right next to "book" but is still allowed to modify "book."
-- Modifiers that are set off by commas are almost always nonessential.
Careful. Sometimes commas are placed in sentences in order to improve clarity.
In other words, not every comma sets off a nonessential modifier.
In addition to being offset by commas, we know that the which-clause is not essential because
(1) Removal of "if published" does not change our ability to identify the noun.
(2) Removal of "if published" does not change the core meaning of the sentence.

• sidebar: the word "tomorrow" in your sample sentence is okay

I am not sure what bothers you about the word "tomorrow."
It presents no grammatical issues. The author seems to be speaking about linguistics.

"Each context" is a little vague but not dangerous.
"Different contexts" would be better.

Redux: An Exception to the Touch Rule

The COMMA + WHICH modifier usually requires that the noun it modifies be placed immediately before the modifier.
If an essential modifier follows the noun, however, the noun can be split from COMMA + WHICH — as long as what "which" should refer to is clear.
In this exception, "which" is not adjacent to the noun it modifies.
-- right next to the noun "book" is the modifier about how different people use the word “tomorrow” in each context. That phrase is an essential modifier (and a long prepositional phrase )
-- the words "which if sold" are placed right after that long essential modifier.
-- both modifiers correctly refer to "book"

The "which if sold" clause is allowed to modify the noun "book" because, as I mentioned above, essential modifiers trump non-essential modifiers.
We have an interesting (and long!) prepositional phrase that is essential to the identity of the noun and that cannot be placed elsewhere in the sentence.
We have a which-clause that gives us some extra interesting information about the noun "book."
The "about . . ." phrase and the "which if published" clause cannot both be in the same place at the same time (cannot both be right next to the noun "book").

This sentence thus follows the pattern in which an essential modifier can and often must be placed between the noun and the COMMA + WHICH modifier.

The "which" can "reach back" and over the prepositional phrase ("about how different people use . . .") or other essential modifier (such as an appositive).

Typical Structure: NOUN + essential modifier + comma + which

If there is a second noun: X + preposition + Y + COMMA + WHICH

Almost always on the GMAT, X and Y will be different, and this difference helps us understand the noun that the which-clause refers to.
(e.g. singular X / plural Y) that the noun to which "which" attaches is clear.
For example, in X of Ys (a flock of birds), the X element is singular and the Y element is plural. The verb following which will be singular or plural and thus will tell us whether which modifies X (a flock) or Y (birds).

Another way that X and Y can be different? X will be a thing and Y will be a person (the signature of Ms. Smitih).
-- In that case, which would refer to signature because "which" cannot apply to the person = Ms. Smith = the Y element.
A good example is in this OG 2018 SC about Emily Dickinson's letters, here.

In that question, SPOILER ALERT

Here is another example from OG Verbal Review 2018, SC # 192 (SPOILER ALERT - beneath the spoiler is the answer to an official question.)
Global warming is said to be responsible for extreme weather changes, such as the heavy rains that led to flooding throughout the state of California,

• Final comments

The question you asked about the sample sentence highlights an important exception to the noun modifier "Touch Rule."
What is the source of that sentence?
The sentence is a good example because its (essential) prepositional modifier beginning with "about the ways" is very long—but the which-clause is still allowed to "reach back" over that long phrase in order to modify the noun book.
I ask about the author of the sentence because the phrase "in case is published" is not standard.

I hope this analysis helps!

*Compare, for example, "Some people may have also had answers to their security questions stolen, which, if published, could make it easier for hackers to gain access to other accounts that use the same security answers. Atlantic Monthly, "Yahoo Suffers History's Biggest Known Data Breach Yet," Dec 14, 2016, HERE (accessed 09/27/2018). The Atlantic is among a few journals with beautifully written prose and nearly flawless editing.