I have a few tools just for this. I use an ultrasonic knife, a hotknife and an electronic sander. The ultrasonic is for small detail work as it takes almost zero force to cut one of those runners. The hotknife is for larger structural part. Since the ultrasonic cutter has a built in "cooldown" mode, the hotknife can step in. Unfortunately it does not work well with small parts as it will shatter/deform the resin.

The reciprocating sander is from DSPIAE models and it allows me to clean up the parts after removal.

I'm working in 700th scale BTW...

-Regards