okay so im making this sweet GRP but it has to be a reaver, so i need to learn 3 things.
-Can i change the code and weapons to make it fire normally?
-Can i change its speed
-can i change the unit size (like how marine is small, and bc is large)

thanks

Not from what I know.
Yes
If I am understanding you right sure.

I messed with the first one in the past and never got it to work, but I'm not exactly a stellar modder so don't take my word on it.

The second two you can definitely do (if my memory serves me correctly).

i got the second easy, just change the move in Icce or what ever its called. But couldnt you just take the text from one unit and paste it to the other but keep the moving section?

no, because they call different framesets which might not exist for that unit and create a crash.
a reaver should be able to attack normally if you make the attack animations normal in IceCC, delete the scarab button and normalize the attack button in firegraft, and then give the reaver attacks and different ai commands in DatEdit.