The branch difference from devel and '1.4.0rc1' was unclear for me since now, now I have learned a new piece!
BTW don't worry, I've spent last 35 year working with computer(s), but I'm not a programmer 
Fast path to go back is to have 2 SD... or reinstall OctoPrint in 4 mins.
Thank you and regards.
Leo
Absolutely. I have a library of microSD cards and a database to know which one holds what.
Got it.
Thank you!
2019-11-28 19:58:11,534 - octoprint.startup - INFO - Starting OctoPrint 1.4.0rc1
This is really great ! I will test right now.
I would suggest testing 1.4.0rc2 instead
Yes, of course. I will take the latest RC available. Thanks for the hint.