I know this sounds ridiculous, but how do I change the mayor registration text in the splash screen? I never received that option when I first launched the game, and I'm kind of a weirdo when it comes to these things.

Where would that configuration file be located?

I'd have to look for it with a hex-editor.

Using a hex editor to modify the SC2000 .DAT file, the mayor name can be found around offset 0x001E563D and the company name at 0x001E565D. Perhaps Boxer's bundler could be expanded to allow for patching, with text fields for entering the new values on GoG's launcher menu.