In simple terms, there are two kinds of screen in Mame - 4:3, and 3:4).
Bezels can be any aspect ratio - 4:3, 16:9, etc.
If your source files (your wallpapers used as a bezel) are 16:9, then in essence you need only two LAY files. One that is for the 4:3 games , and one that is for 3:4 games.
So yes, you'd actually have 80+ lay files, but there'd only be two variations. So no need to edit them once you've created them once.
The only time you can get into trouble is if you want to change the size of the bezel in relation to the screen (game) size. If you do that, then yes, you'll be editing LAY files for each variation.
For me though - since I knew I'd be creating quite a few Bezels - it made more sense to institute a "standard" I would stick too. I set myself a standard Bezel size, and designed the Bezels to fit that standard. Doing so meant I could concentrate my time on creating the artwork, rather than messing with the LAY files. I essentially created two LAY files, and two template Bezels (four files) and used those over and over. Once set up, is was very simple to do.
I toyed with the idea of writing all this up and posting it for people new to Bezel creation, and at one point wrote something - but for reasons I don't recall, I didn't post it. Of course, now I can't find it.
Perhaps it's something I should do for the benefit of others who come later..........