landing gear doesn't matter, since the CG is much more important in the air. depends on the type of plane. trainers generally don't offer much to easily move around, but they also don't need much adjustment if you use the recommended engine size.

to get the cg right on my stinger 1.20, i had to move the firewall back 1.5 inches, move the servos to the rear, and install a hatch in the back for the battery. (pretty extensive mods)

and finally, you ALWAYS want to move functional weight before adding weight. if you can shift a battery pack, go for it, at least before adding lead. or use a larger pack/better servos/etc... if you have to add weight, add it as far out as possible to the needed end. (weight on the end of the vertical stab or a heavier spinner)