Stats reset after any change in the stat itself, easiest example is just unequipping or equipping a piece of gear. The stats go back to what they were before the editing. The temporary changes the trainer does do affect battles, its just that their temporary.
Stats only or also maximum health? PLease watch my demonstration video from previous page and verify that maximum health change persist (or still reverts, but in this case also tell me if you do something different than me).
As I've got the feeling that stats are bound to the level while maximum health change persists.