Rename files that exists under a directory that matches criteria

[Mitiraj]

All,
I want to rename all files that exists under a directory and matches the criteria.
For example:
1. If the file name is 300.xls then the new name should be test_admin(300).xls
2. If the file name is 400A.xls then the new name should be grid_admin(400A).xls
3. If the file name is 420A.xls then the new name should be office_admin(420A).xls

Experts , need your help with code. thanks..