Installing a custom rom on a fascinate metroflashed to metropcs

[lamborinimustang]

I want to metro flash this phone to metro using metroflash (legal look at metropcs.com and look up metroflash) and i want to install a custom rom, but i'm afraid if i do so it might unflash my metroflash service? should i do it before i metroflash or after? is there any compatible roms for a metroflashed fascinate? if so tell me.:'(