If duet folks are interested in trying what was built as a proof that this would work: https://github.com/smartavionics/Cura/issues/8 is a feedback place with builds that add this feature in to a test version of Cura. It adds in a checkbox to mark the printer as having a shared heater. The checkbox then alters / blocks the behaviour of any temp change calls which would adversely affect the currently selected tool. Is that right @burtoogle ? Please test, feedback and comment in smartavionics GitHub directly if you get a chance to test. I have been printing all day - small models which turn off various tools and change the temp of different tools all good for me.