Consult a qualified immigration lawyer... Don't leave immigration issues upto to the feedback you get from strangers on the internet... If I or any other forum member tell you not to worry and go ahead with switching to F1 and you lose your visa status no one but you will lose sleep over it... my 2 cents.
His company lawyer already advised him against it.
I have spoken to multiple "qualified" immigration lawyers and no one has a guaranteed definite yes or no.I have gotten different answers from different immigration lawyers.
Your individual situation/immigration status/case/paperwork/attorney has more bearing on the situation than anything else.
There is no clear yes or no answer to this question.
In addition to what MBADreamzzz said, I would say that consult a qualified and well known lawyer and don't hesitate to consult more than one immigration attorney as the H1B to F1 conversion with I-140 approved is a tricky situation that many lawyers are not familiar with.
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