Unique Remittance Number under Manage Installments need to be made mandatory for certain BUs'

In our project we are using custom roles only but they are not segregated at BU level. Same role eg: for Invoice Entry is used by all BU and the data access is provided to the user as per the BU they belong to.

Now few countries have a requirement to make the Unique Remittance Number under Manage Installments as mandatory. We tried using sandbox to customize the page but its not working at business unit level expression builder. The custom role expression builder is working but we wont be able to use it as the same role is being used by other BU as well.