Overriding mouse drivers to enable left-handed button layout

If you want to permanently switch the mouse buttons and software wont let you do it, then you can try to do it in hardware.

Of course, this all depends on the mouse hardware itself, but you should be able to desolder and resolder the wires connecting the mouse button's intermittent switches.

Apparently, if you want the mouse to work as intended in Windows, you go to people doing file system drivers.

Moure, a part of Ext2Fsd project, actually makes left-handed mouse work flawlessly on all of my benchmarks.

Granted, it runs in an actual window and there doesn't seem to be any way to have it automatically run at startup (or automagically mark every mouse as left-handed) changes system-wide drivers that affect all Windows users (instead of a single user), but it actually works.

If I find any issues during my use, I'll update this answer.