Assuming SNES9x has the same functionality on Mac as it does on PC, which I believe it does, all you need to do is rename the patch to have the same name as the ROM (except for the extension) and put them in the same directory/zip file.
For instance, if your ROM is named SUPER MARIO SUCKS COCK.smc, then you should rename the patch SUPER MARIO SUCKS COCK.ips and SNES9x will automatically soft-patch the ROM during gameplay, no hard patching required.
If you really want to hard patch the ROM, meaning you permanently want to attach the patch to the ROM, you can get one of the Mac patchers from here:
http://www.zophar.net/utilities/patchutil.html
Be warned, using a Mac has been proven to make you 64% more likely to contract the HIV virus.