Is it bad practice to write to the registry?

just for settings later and using a standalone executable with no way to remove it? Because I did, I do, and don't care. It just works.

Windows filesystem structure is so fucked up that they need to duplicate the filesystem on a more uniform bloat bag, the "registry".
FACT

Just look at how WINDIR looks like the crude output of lots of different builds. I even found some buildlog.htm in there.