Hello,
How about:
Create a new configuration "segment" to create a nice new user with the appropriate privilege level and services etc.
Apply this to a couple of switches and test
Create a new ssh template (please stop using telnet :-) ) with the new credentials.
Start using the new template with the pilot switches.
When happy apply to 5, then 10, then 20 and then the rest in one hit or in multiples that suit you.
When complete use a new configuration "commandlet" to remove the original user.
Delete the old template from iMC.
Something like that.
Cheers
Ian