About mess (using a rom of mine)

[luckiejacky]

Can I use a rom image of mine to replace (let's say avance logic) the tseng bios for at486 emulated machine?
And also if I need to use radeon9600 (just kidding) in the future, do I have to modify the source code myself. I mean it won't work by just plugging in another rom and it wouldn't work?

Another question,
When I plug in ss20_v2.25.rom for sparcstation 20, it says it is not recognized.
Why. Also, when I have a rom pack downloaded somewhere with the filename mame*,
and I want to start up a at386, it says et4000.bin is not there while I am actually having it.
Thanks
Jack