Reverting back to a default resolution in mame

[Rogles]

I have an arcade cga crt set up in vertical orientation and a windows 7 machine. I downloaded crt emudriver and got the cga vertical games to display properly using 1280x0 (2560x0 doesn't work for me - switchres isn't liking it) in the mame.ini file.

I'd also like to have a handful of horizontal orientated games to play on the vertical monitor, though they don't scale down well at 320x240. I've found that 640x480i looks better for them so I set up a game specific ini file which sets the resolution to 640x480 and tested it. So groovymame fires up at 320x240 and when I select the horizontal game, it switches to 640x480. The only problem is when I exit the game and go back to the menu, the resolution stays at 640x480. I'd like it to revert back to 320x240 however I'm at a loss as to how to do this.

Also, does it sound like I'm doing this the correct way? Or should I be messing with vmmaker and the modeline stuff (which I'm having some confusion over).