How to get Add'l Period of Service Det's DFF to appear in MSS based on context?

We want to make the Add'l Period of Service Det's DFF context sensitive. We have tried c_legislation_code and business_group_id. We would like for the fields to appear in MSS based on the context. Even though we can tell that the business group id is recognized in MSS, the DFF fields are unavailable. How can we get them to appear? My understanding is that we cannot add a context to the Add'l Periods of Service Information DFF because it is seeded and would be wiped out upon upgrade. The contexts for this DFF are recognized in MSS, though, so we want