You will want to use EVPM to do that. Unless you are on EV 6 and all the users are in the same OU. You can change the policy by OU, but that will change for everyone in that OU, so most likely you are back to evpm.
The quick and easy way to get the distinguished name for the script is to run a report mode for the users you want to change. Open the report in Excel and there will be a column for the DN.
Regards,