or if you want apply this resolution for all games, you can with AtomicFe do like that:
Open AtomicManager to load your config.
On the "Folder" tab , in the Default Emulator field, you shoud have something like that :
C:\winmame\mamepp.exe
just type in the field behind the emulator : -resolution 1024x768 (or -r 1024x768) to have something like :
C:\winmame\mamepp.exe -resolution 1024x768
Save and quit.
Now Atomic should run all your game in this resolution.