@Dynamite With A Laser Beam
Not to my knowledge, no. As far as I can tell, trying to change/modify an ability of an existing unit would result in ALL civilizations getting that bonus.

(And yeah, it's a bummer. Extra Great General range would be really appropriate since that's what he had in the game. Unfortunately I work with what I have.)

Is there no way to make the great general range bigger at all? Or is the game's code just too funky