I am facing a situation where I need the on-board micro-USB of the Teensy for other purposes, but don't want to lose the ability to connect to PC, including for dev/debug over COM.

Is there an example of anybody using any of the non-USB serial

for debug including sketch upload?
Say, with an off-the-shelf USB-to-serial adapter: USB attached to the PC, serial attached to Teensy?

Is it just a matter of making the Teensy Serial# show up as COM on the PC, or are there other constraints e.g. on sketch upload?