Assuming OpenSRS is unable to actually change an RSP's username (It may be a primary key which cannot be easily altered), as a workaround, talk to your sales droid and ask them if they'd be willing to do a free RSP-->RSP transfer for all domains in your current profile to a new profile.
I asked about this a few months back (for an entirely different reason). Rep claimed it was impossible. As a DBA I don't see it but oh well.
And I seriously doubt they'd give you a free anything. All of my bulk-related requests have been greeted with nothing but cha-ching.
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