I believe that the "Origin client" is a platform similar to Steam that you are required to run in order to play some of EA's games, not including Ultima Online.
As I mentioned before, I'm not sure if the master account you log into when you visit the Mythic Account Management site (i.e., kind of the "parent" account that encompasses one or more of your UO accounts and looks like an e-mail address) is one and the same as the account you log into when you visit the Origin site.
I strongly suspect that these "structures," for lack of a better term, probably ARE one and the same thing, since the account you access via the Origin site maintains a history of your UO subscription payments. However, I think you are limited in what you can do with any such "account" depending on whether you are accessing it through the Mythic Account Management site or you are accessing it through the origin.com site.
For example, if you log into your "master account" on the Mythic site by entering the e-mail address and password, you're able to manage your UO subscriptions and payment methods for those subscriptions, but as you have noticed already, there is no way to change that e-mail address which you use for logging into the "master account." However, if you go to the Origin.com site and log in there using the same e-mail address and password that you used on the Mythic site, you can assign a "persona" to your account (e.g., call it "The Raving Purple Monster") that is independent of the e-mail address assigned to your account and you can apparently change the e-mail address associated with the account as well. However, if you are using the Origin client with that account, you apparently cannot use the origin.com site to change payment information for any EA games that you play through the Origin client; you must make such a change by talking to a customer service representative.
Yes, it's confusing.
I think your best bet is to contact EA and tell them you want to change the e-mail address that you use to log into the Mythic account management site to manage your UO subscription(s).
The original notice we got regarding Broadsword taking over management of UO said, in part, "Electronic Arts will continue to provide billing and account services through its Origin™ portal." This statement, as well as information that is currently available on the Origin site in the Help section (
https://help.ea.com/en/article/uo-my-account-billing-information/ ) make me strongly suspect that at this time, if you were to contact Broadsword for help with managing your UO account, whoever you contact would probably just have to turn around and pass along your request/problem to someone at EA.
The above-mentioned article discussing how to contact EA's technical or billing support departments for help with your UO account was last updated February 4, 2014, which is the exact same day Mesanna published the announcement regarding Broadsword taking over operation, support, and development of UO (
http://www.uo.com/article/Producer-Letter-0). It indicates English support is available by e-mailing
[email protected] and English support outside North America is available by e-mailing
[email protected].
Good luck! If you do manage to get the e-mail address that you use to log into the Mythic account management site changed and it doesn't screw up your ability to manage your UO accounts, could you post and let us know what process you followed?