The save game version numbers didn't change between 1.0034A and 1.004A, and a save made in the latter can be loaded in the former. I'd guess it should be safe to switch back and forth.
If you want to test something in a new game again,
iZakaroN's SaveEditor (or from
Kiya's site, with description) should work to give a large stat/experience boost to a new character.
With the CD/DVD version of the game, you can edit the
config.div file (in Notepad or another text editor) to play at a higher or unsupported resolution. The game itself should be fine at higher than supported resolutions, but opening the auto-map can cause the game to crash (the frequency of which is resolution and system dependent).
