If your CNC machine has a built in Tool Length Probe and a software controllable spindle, you can configure MillMage to automate some of the tool swapping process for multi-tool jobs.
Documentation on Custom GCode:
Device Settings: Custom GCode - MillMage Documentation
Documentation on Tool Length Probing:
Tool Length Probing - MillMage Documentation
MillMage Getting Started Playlist:
https://www.youtube.com/playlist?list=PL5OMg-VCnQ69Z0CdikH0QKdXP3bXMnwUB