It is possible to throw a 24 fret RG neck on, but you'll need to move your
neck pickup out of the way, because those extra frets will need that space. The cost of a used RG neck on **** is usually over $100.
You'll be better off selling your EX, and buying a used RG 5XX. You'll get those 24 frets, an
Edge trem, better wood, and better quality all around.
It's not really worth it to fix up an EX.