How to modify GlueXML files?

I want to change the behaviour of the login screen. Specifically, I want the "Remember Account Name" checkbox to stop getting cleared when I type in another account name. To that effect, I created an MPQ archive with a modified "Interface\GlueXML\AccountLogin.xml" file. Unfortunately that does not work because the game refuses to run:

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World of Warcraft
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Your login interface files are corrupt. Please reinstall the game.
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Anybody knows of any workaround?

1 - Use HD client which got fast login option.
2 - Use Awesome WotLK

https://i.imgur.com/eC13HnQ.png
Just create a shortcut for the game's .exe file then right click the shortcut and select properties , at the target field go to the end leave x1 space (press space once) and write the following -login "LOGIN" -password "PASSWORD"
finally , you can always use shortcut to open the game directly with that x1 account info (i think you can make multi shortcuts with different login info ,so you can use multi accounts)

HD client is best solution so far for multi accounts login, default game client will clear the old one and remember the new one
you can enable read-only so the game doesn't clear the saved account name you use but that may result alot of data updates not to be saved like addons changes/game settings.

Awesome WotLK is a good solution but I already have my own patches :( I have to say though that FlashWindow is something I really, really want. I would have to see how to move my patches to Awesome WotLK, if possible.

The HD client is something I don't want since I want to keep the look of the original client.

Thanks!