I have a group of 900 users who i need to modify

For a application what uses radius it is needed to put the acountname in the DAIL-IN tab section of each user account. In the attribute  msRADIUSCallbackNumber

So this attribute works in a single modifacation of the user. But i need to change 900 of them.

What is the best way to do this ?

Regards

Tiemen