Hmm, what about the permanent bonuses from the books? Is that lost when you alter a Edit a character's level or can you add the boosts? You can always just give yourself a lot of books, though, so it's not like it really matters.
I had a look and found where the stat boosts from books are stored in the character data; it's a few bytes beyond the subclass skill levels. These
are editable and taken into account on level up, so while you can't directly edit the stats, you can edit the boosts and thus influence most of the stats (STR/TEC/VIT/AGI/LUC) that way. This even appears to work with boosts set to a value higher than 10, which would be the maximum the game allows per book, per character: I set my Landsknecht's to all 255, leveled her up once, and the game happily accepted the values, with all five stats now being 99 (can't override this cap). They even stayed at 255 internally afterwards (i.e. weren't forced down to 10 by the game) according to a RAM dump after level up.
I'll experiment with this a bit more, and if I can't find any negative side-effects, I'll add stat boost editing to the editor for the next version. I'll also add a note that changing these values (as well as
probably the level, all things considered) will require the character to level up once for the changes to actually take effect.
Edit, another test: forced Landsknecht's level back down by one to 74, forced EXP to require 1 more EXP to level up back to 75, set the stat boosts to 20 each. Result after level up? STR 87, TEC 62, VIT 82, AGI 73, LUC 53, while the base stats on level 75 are STR 67, TEC 42, VIT 62, AGI 53, LUC 33. In short: it appears to work fine.
Edit 2: New build v1.2.1 released! This removes the non-working direct stats editing and adds stat boost editing instead; it also adds map image exporting. Hopefully this'll work correctly now.