If you only want to force reason codes for one group of people, you can do the following.
On "change sys feat" change the "Aux Reason Codes" field to "forced."
Then, on the stations of all of the people that you DO want it forced for, make sure that their "Aux-work" button has nothing in the "RC" field. When these people press the "Aux-Work" button, it will ask them to "Enter Reason Code" on their phone display.
Next, on the stations of all of the people that you DON'T want it forced for, make sure that their "Aux-Work" button has a "0" in the RC field. When those people press the Aux-work button, it will automatically put them in Reason Code 0, which is default.
After that, you'll want to go into your CMS and add the Dictionary names for Aux Reason codes so that you can see them on the reports. Otherwise, you'll just see the 1 digit number.