I did just that, but now the OT trash bytes are invalid, and the nickname trash bytes are valid, but it says that they're from a German/French/Spanish game, despite being from an english game. I know that the problem isn't in pokecheck or pokegen, as you were able to get a valid one, and pokecheck verified this. I'm also running version 3.1.13 of pokegen, the latest version. Something is wrong with my trashbytes.exe or I'm just doing something wrong (the more likely of the two).
After re-naming Umbreon to Cornell and running it through trashbytes.exe I got this...
https://www.pokecheck.org/?p=detail&uid=3841243