@dc42
Is there a simple approach - maybe in future Firmwarereleases - to zero out/reset all csys in the config-override.g when homing or restarting (I think homing would be enough? (Was my fault that I didn´t check, that the NIST-Standard, that you quote for following, on additional csys is that way, that they seem to have to get saved for next startup...) sorry for my bad english!
For now, all good: I might just zero all csys after G54 out either in the config.g or when homing... The trick with the homing I might put in the g-code-wiki, to remember people (like me 🙂 ) that csys vals are saved in the confg-override.g