WBS settlement rule enhancement

Dear experts,

Could you kindly help on the WBS settlement rule issue.

The PS project has several WBSs, one WBS is used to collect expense. The costs of this WBS are not allowed to be settled to AUC.

The costs of other WBSs will be settled to AUC.

I need to know, if there is an enhancement or other way in SAP to prevent the WBS from settling to AUC.

Thank you very much.

Judy