Not to rain on the Pookie Parade or anything, but you shouldn't make all of the changes that you suggest. Otherwise, *you* may be the recipient of a red-inked paper.
"In addition to your LSAT score and academic achievements; your personal statement, book essays, letters of recommendation and extracurricular activities will weigh heavily in the decision-making process."
I know semi-colons are great and all, but don't misuse them.
It's not misused. The semicolon introduces a list. This semicolon prevents the sentence from being misread.
There are only two items in the first list and no comma is used; thus I don't think a semicolon should be used. A semicolon makes sense within a list when you're separating list items that contain commas themselves, for example:
This summer, I traveled to Phoenix, Arizona; Las Vegas, Nevada; and San Francisco, California.
Forgive me. I didn't provide an adequate explanation. A semicolon is appropriately used when used in place of a comma (that would otherwise cause misreading), which I'm sure that you believe should follow the dependent cluse "In addition to...." If the semicolon were not in place, the sentence would read that in additon to your LSAT, academic achievements, your personal statement, book essays, etc. As you can see, that is definitely incorrect.
The example you gave is exactly correct; but, does not apply to this case.