Why can't I use a cname/alias in the permissions table?
Plan A:  If dull and shiny don't change, leave both in effect?...

GRANT ... TO dbuser@dull ...;
GRANT ... TO dbuser@shiny ...;


But, beware, this could leave the "production" system accessible to "QA".  (Assuming that is really what you are doing.)

Plan B:  A simple script (after transferring):

UPDATE mysql.user SET host = 'shiny' WHERE host = 'dull';


But, again, beware -- If the script fails to be run successfully, QA could be hitting production.

Plan C:  Well, there is likely to be some other trick.