Hey! I've been researching a bit, and I've found out a lot of details about the .sav format.
A screenshot is included to demonstrate what I can do so far. Do not hope for a .sav based level editor, but a really advanced .sav editor might come.
So far I have documented:
The flashing landmine object. I get it to activate, deactivate, trigger an explosion, and change its pattern to an all-red one.
Mudokuns are partially documented, and I can change their position, direction, scaling, coloring etc.
Abe is partially documented, it's in a slightly different format than other muds.
"Blockers" (Like on the screenshot) are partially documented too. I haven't managed find their object sizes.
Limitations:
Some objects, like landmines and blockers, can't be moved to any position, but to pre-set positions defined by the levels.