Finaly managed to fix my two issues.
A little reminder:
All begins when I want to remove the 127s for putting back my 110/137s.
Impossible to remove the right 6mm crank bolt, everything I try just damage the hole more and finally it gets perfectly round.
The cause: WAY TOO MUCH LOCTITE+ bad quality tool in the first place.
Solution: hammering a T45 Torx key and heating the bolt during 60s with a blowlamp to break the loctite.
So, I finally managed to avoid the not so sexy “cut the crank” solution, and removed this stuck bolt, but… when I started to install the 137, everything was going well until I try to screw the gold button.
I feel a big resistance and I try to force it (second mistake).
Issue 2 : the thread of the shifting shaft is damaged and so the gold button is.
The cause: The hammering must have deformed the head of the shaft, and by forcing the bolt to be screwed in it damaged both the shaft thread and the gold button.
Solution: Bought a set of thread cutter (and a pair of buttons) and restored it this afternoon. (thanks to florian for all the advice on emails)
It would have been very simple if the shaft was not freely spinning inside the hub. this is how I blocked it while screwing the thread cutter:
The 3 m4 nuts were a good solution to keep the shaft from spinning while I was screwing the thread cutter in the other side, but unscrewing the nuts or the cutter when it was a little stuck was the complicated part.
Anyway, I managed to put the 110/137 back and gave a quick test 1h ago on my parking (137 hole) and found it way easier and stable to deal with the 2nd gear than with the 127s.
The shifting was good as soon as I installed my weird spoon system on my shoes (weird but efficient) , but now that all works fine I will probably pull the trigger for a pair of Five Ten shoes.
A last tip:
Before this two issues I was worried by a strange noise (crwik, crwak) while riding.
The cause: It as just my hub needed some special grease.(second hand that has not be used for a long time by its previous owner)
Solution: added the syringe of grease that came with the g26.
Since, I ordered a set of syringes from florian and just put another half syringe to be sure just before my quick test.
Hop this will help.
So remember: DO NOT USE MORE THAN ONE DROP OF BLUE LOCTITE if you decide to use some.
If something goes wrong: NO NOT FORCE before knowing what is going on.
If your bolt is stuck and you apparently can’t remove it DO NOT CUT YOUR CRANK before being sure there is nothing to do.