I mean, the ability to disable undo entirely from Lua tools would be kind of ‘dangerous’, especially if a tool was somehow faulty…then undo would suddenly have been disabled for the remainder of your Renoise session, not good…
Disabling undo will also quite easily break down the whole undo/redo logic and thus Renoise. If you for example suppress undo for the insertion of a track, but not for something else that you later on are doing with this track applying undo/redo will sooner or later crash.
So no, we can’t add that and have to solve this differently.
When the tool changes track colors, this always should have been in the undo/redo chains. Not sure why it wasn’t in 3.0.