#1
Would it be possible to substitute my squire strat neck for a jackson neck with a reverse headstock? i will shave off the extra frets. so i have that solved, but will the neck fit in the pocket?
#2
Its critical that the scale length is not changed. The scale length dictates your fret spacing, and you find it by measuring from the nut to the top of the twelfth fret, then doubling it. That will land somewhere on the body and its very important that your strings anchor point are there. Its very possible that you will have to move some of the squire hardware o make this work.

What do you mean shave off frets ? not a good idea.....
#3
I have asked in a music store about it fitting on other guitars and from what i heard they won't at all, but as far as I know it wouldn't work. Fenders and Squires have a rodded neck that's not set, and pending on the jackson they have varied necks. So, it would depend it you had the right one.

A flat ended c neck with rod might work. Anything else, probably not.
#4
#5
Doesnt look like taking off the overhang is going to get rid of enough frets. The squire neck I have is 22 frets with the 22nd fret sitting just where the heel of the neck is and a bit of fretboard overhang. A 24 fret neck will probably be the same so to get it to fit your gonna have to cut part of the heel off to, about 3/4 of an inch. The truss rod could complicate trying to cut off that much wood. And moving the screw holes for the neck plate that much might present problems to.