What I've done before is import the full MAME set including e everything and then use Genres. Basically, use the auto create playlist's function and then go to Genres. It automatically separates games into computers, consoles, slots etc. From there you can just select all (alt a), right click and use bulk edit to change the platform for all the games under that genre. Thats how I know have an entire full MAME set but nicely separated into different platforms.
On a side note, nobody really talks about it, but MAME has a TON of goodies in it that are not arcade. Most people only care about arcade but some things in MAME are fascinating and really fun to explore and play with.
Retro_Rage's post in MAME - import just fruit/card/quiz games as separate platform to arcade games? was marked as the answer