User Group Name change through sql query

[ravi]

Hai,
We have a mail parser, which creates tickets and places them in a department.
Some of my tickets doesn't have the user group id, due to some problem(have any idea, when it happens ?). So these tickets are saved with user group id name "Registered". I want to move them to custom defined user group id using sql query.

I want to know is there any side effects of this on kayako db and what tables or fields i need to change, if using query i changed from "Registered" to custom value.
Any other way through kayako GUI to change them