Thump...thump.... "rapping on the side of the universal translator"...

whoooweeeeeeewhoooop....

"What do you do with the modification parts that are left over?"

I never throw any functional bits away. Switches, motors, gears, and cable connectors are put away until another project may need them. I usually don't hang onto the generic large pieces of plastic. I may hang onto the smaller custom plastic pieces.

My other hobby of building 1:6 dioramas causes me to hang onto all sorts of odd things in various scales.

This lawn tractor was originally a much smaller scale front end loader.

You never know when you'll want to build a patrol boat out of the snow sled, PC case cover, clementine crate, and broken plastic clothes hanger. 

ScottE -- Member (always) & Moderator (when needed)