How do we add user-defined formats?

I want to track LXO, MAX and other arbitrary formats. How do I add them? THere's no need for preview generation.

I noticed the old method of modifying the custom.txt file is still sorta functional, but any new formats added to it show up under one unlabeled file type in the "File Type" section of MP. Not very useful.

BTW, for what it's worth, I'm a user since the iView days, dipping my toes back in here because I have specific needs for a good, stand-alone DAM.

Thanks in advance,

-Sebastian