I am not sure, if this is of any help, but, please, note that in PT 8 you can (at least in theory) change the username by using Convert Project tool. For details, see PT 8 help:
In Paratext 8.0 (and later), you can replace the names of users on a project with the names of other registered Paratext users. This is useful in a sensitive location where pseudonyms should be used instead of real names:
Open the project whose user names you want to change.
From the Tools menu, point to Advanced, and select Convert Project.
Enter a unique name in the "New Project short name" box.
If you have edited with Paratext Live, select Clean up Paratext Text history.
Select a user name from the "Replace old User Name" drop-down menu.
Enter a different registered user name in the "With" box.
Click Add.
Repeat steps 5 through 7 for the users whose names you want to replace.
Click Convert. Paratext creates a new project. If you want the new project to replace the project with the former user names, follow the instructions in How do I permanently delete a shared project for all project users? Once the project with the former user names is permanently deleted for all team members, have them Send/Receive and use the new project.
Changing user names will replace former user names in the following places:
Note authorship and assignment: Select Open Notes from the File menu, select the converted project, and open any note.
User names: Select Users, Roles, and Permissions from the Project menu.
Project History: Select Project History from the Project menu.
