depends on the aircraft.

R/C trainers are designed to be spin resistant, and self recovering. (Like the full scale Ercoupe is virtually spin-proof) Some models are as hard, or harder to get out of a spin than the full scale planes they are representing.

Changing the center of gravity rearward, and adjusting both of the ailerons downward (2 to 3 turns on each clevice is a LOT... and will make snap-rolls tighter.) will make your trainer behave more like the full scale aircraft, making it require positive action to recover from a spin. But... be careful, you can make it impossible to recover from a spin if you adjust things too much.