The CATT command by default do not have option to change the Spec using the pulldown.
To accomplish this RegCompDlgs.dll has to be modified.
Follow the steps below to get the pulldown to update the specs.
1. Go to Project root and open Project.ini file
2. Find USECUSTOMREBCOMP field and change it to 1 and Save
3. Extract the attached RegCompDlgs.zip to Project Root%Standards/..
Note: rename or copy/backup the orignal RegCompDlgs.dll to a new location
4. You should be able to now change the Spec through CATT dialog
AutoPLANT versions prior to AutoPLANT V8i should have there RegCompDlgs.dll upgraded before performing this action.
Please see below link to upgrade RegCompDlgs.dll.