Unfortunately, editing your stats (or just cheating for XP and getting them to shoot up quickly) seems to break your Main level.
You can have 20 in all stats, but for some reason be stuck at Main level 19, without any way of increasing it.
I think it has something to do with the 2 stat increases you get at the start of the game. When you use the trainer, the game seems to forget about those, and your main level actually drops slightly because of it. So if you take a point of Strength at the start, and use the trainer, it will end up negating that point. So you would start with 2 Strength instead of 1, which starts off calculated into your Main Level. But with the trainer, it doesn't seem to get calculated properly.