So it's actually a bit of a pain in the ass to figure out how to register this fucking game. I did about 30 minutes of digging on google and came up with this post, which details (almost) everything you need to know
https://www.reddit.com/r/rpg_gamers/comments/3u8b6v/any_realmz_fans_out_there/d35uui7/
In order to reset the serial number, you need to type 410 into the registration code area itself, then enter the new serial number when prompted, then enter the registration code. There's no button to reset the serial number.
I also found some information on the game mechanics
https://fantasoft.powweb.com/HTML/Realmz_Files/Realmz_HTML/Realmz Manual/Manual Files/chapter_6.htm
Note that there are only two genders, and that men and women have different stats, so the codex shouldn't devolve into shrieking and shit-flinging about the gay agenda. However, there may be some Jews in the game (gnome cabalists), so just be aware that the game might be trying to mind-cuck you into wanting a pair of yoga pants and a topknot and other instruments of the (((globalist))) agenda. You have been warned.
You can get the game here:
https://www.myabandonware.com/game/realmz-bce
I'm still looking for a way to fix the resolution so that you don't need binoculars to play. If anyone has a lead on that that'd be great.