Good question. To the best of my knowledge, no syncing is done between MNet servers except when user from Moodle A attempts to login to Moodle B.
So a Moodle A user (hpotter) is a unique user. If the user name in Moodle A is changed, then Moodle B wouldn't be advised of any change and probably try to register the user as a new user. EMail address changed as well?
One way to find out for sure: create a user hpotter in Moodle A, enrol that user in a Moodle B course via MNet. Make sure hpotter does participate (post to forum/take quiz, etc.). Change hpotter user name in Moodle A and see what happens! ;)
If the system won't do it, the 'backdoor' *might be* to edit mdl_user table on Moodle B to match changes made on Moodle A.
'spirit of sharing', Ken
I also think a new user would be created. I haven't tried with Moodle but this happened to me with Mahara Mnet when one of our staff got married and I changed her username in Moodle -when she went to Mahara it created her a new account. (So she's stuck with her maiden name)
A new user is created. I found you can use the web services to change the username but you need to know the users internal moodle user table id.
thank you, Herb and Mary for your responses. That's what I feared. So every time I change a username (what should hopefully not happen that often), I have to do an mysql query on all remote Peers like that:
UPDATE mdl_user SET username='newusername' WHERE username='oldusername' AND auth='mnet';
I also think, deleting a user is quite difficult: I can't delete MNET users, I only have the possibility to "Deny access". I will also have a look at the web services, that sounds promising.