Changing Launchpad username, and How to know what sites will be affected?

I am setting up my developer profile on Launchpad, and would like to change my username so it would be same as other sites I use, as well as better reflect me as a person. (that's a much more important thing than it sounds)

I want to do this now while I can, because as I understand it, once I set up a PPA it will be impossible to change it due to the username being locked into the PPA URL's to prevent breakages and other problems.

But when trying to change my username, it warned me with this message.

Changing your name will change your public OpenID identifier. This means that you might be locked out of certain sites where you used it, or that somebody could create a new profile with the same name and log in as you on these third-party sites.

How can I find out which sites will be locked out, and how to still change the username while preventing problems with other sites?

Sorry if this is actually a question for Launchpad itself. But I don't know where to post questions like this on the Launchpad site.

Edit: I understand that it is an issue with OpenID. But how am I to know what sites will be affected? And how do i fix the problems this will cause? Can't I just reset the password (and as a side affect, re-establish the connection with the new username) using my email address?

Solution 1:

If you get the message

"Because you have a Launchpad account, you need to change your username from Launchpad."

from https://login.launchpad.net/, go to https://launchpad.net/ and go to your profile and then click on "Change details" (leads to https://launchpad.net/~[[username]]/+edit )

Here you can change your username, but you will get a warning:

Changing your name will change your public OpenID identifier. This means that you might be locked out of certain sites where you used it, or that somebody could create a new profile with the same name and log in as you on these third-party sites. See https://help.launchpad.net/OpenID#rename-account for more information.

Click again "Save anyway".

Solution 2:

On login.launchpad.net you can see a list of sites you last authenticated to.

How to change your username without problems actually depends on the sites where you used the Launchpad OpenID. Most sites let you authenticate with your email+password even if you set up OpenID, so you should have no problems at all.

I'm not aware of cases where this is not true (though, technically, it's possible).