Well, I checked the new APPDATA is for the currently running bash only. I wouldn’t like to break anything changing the global user variable.
@calmh, on first run a folder Syncthing is created in the stick in Program folder, beside 32bits/64bits folder.
I didn’t use -home because I didn’t understand how it works. Now, just trying --home it’s all fine. I added a check to exit if the batch is ran from c: or d: : I don’t know why (maybe I double-clicked a copy of the batch I had in my hard-drive and I didn’t remove in it the APPDATA redefinition, I got a system crash from my firewall driver.sys - this sometimes happens when burst prompts occur on my poorly responsive XP machine - on reboot I ended in a %users%\TEMP profile 
- I got rid of this closing the session, switching to admin, have a look in HKLM\winnt…\ProfileList\ where I saw my own entry with a .bak suffix => renamed, close admin session, log in as Me OK 
)