If you end a level charging a grenade/rocket etc., you can let go during the end of level screen and have it explode on the new level.
I'm sure if you were good enough to use that to cheat, you wouldn't need to cheat : p
OMG! They're attacking a different wall!
Move more troops there!
Again and again and again.
Might be able to be developed into a half decent game, but as it is it barely even is a game.