If most of the essay material is covered I think its manageable - I certainly reused most of my essay materials for each school and got accepted everywhere I applied. I did spend time on the essays making sure they were coherent and specific to the school, and within a few words of the word count.
Its definitely manageable if you have a strong enough profile - I stated the unique part of my profile up front that I guessed would be highly attractive to the adcomms so that everything after that was just ticking boxes...
IF you dont have a highly attractive profile (i.e. you're in an over represented demographic/industry) and no unique work/extracurricular activity (you're not an olympic/professional athlete/founder major non-profit/set up own successful business/worked for some unique firms in unique roles) then its going to be more challenging and you may wish to really make your essays glow...
Sorry its not overly helpful but it really depends on how good your current essays/profile is that could make a quick turnaround work?