For some (certainly bad) reasons, I have put my production server to bêta channel... I'd love to come back to the stable channel, but as it explained on the wiki, there is no way to do it (yet) and I understand why (data structure).
"Yes but"
We have only 2 choices : "bêta" and "stable". Why not to implement in a next bêta a new option, which could be "bêta until next stable" ? This way, it could permit to align the the data structure at D-day, and then the setting could automatically fallback to "stable" 
This is the only "clean" way I see but if another one exists, or another approach for this problem, please let me know.
Thanks for reading, have a nice day !