@raycomp
Usually the pre-compiled novelty voices found on the internet (eg governator) are based on English_American_.vpn and should be so named (Note: it's '*_.vpn', English_American.vpn won't work i think) and therefore as you've found two voices named the same won't both work.

Renaming to another unused voice might work and often does but with unexpected wrong prompts sometimes. Unless you've actually replaced that voice's correct prompts with your own custom recordings from the start as roger1009 suggested.

Because you replaced the American sound files, only it's original name will work for sure with your custom prompts in the right place, and I've found that even renaming to English_British_.vpn can have problems or just won't work (not the Borat [kazakh] one though 'coz it was compiled using the Brit original i think).

It might be easier to start again using a different unused voice file as a basis if you find simple renaming doesn't work. Or you could just use the Pommie one for guidance if you get sick of your own voice.