How to switch off resource costing selectively depending on the work definition type?

Summary

We have a requirement to selectively switch off costing depending on the work definition type(Standard or Alternate) used in WO. What this means is E.g. in standard work definition we have resources R1, R2, R3 & R4, with R2 being the primary/principal resource, it drives the production run rate & entire cost of the operation is loaded onto it. Nonetheless, except for R4 which is labour both R1, R2, R3 should be scheduled as we need to collect them all & perform planning(Supply Planning & Production Scheduling) in a constrained manner. So, switching off scheduling for R2, R3 is