How to pass diff attribute in group by attribute of aggregate operator as per config file iteration

Hello,

I am building a profile on the different scenario like
Customer
Customer Beneficiary
Customer Beneficiary Risk Profile
These three combination present in my config file I want to build all scenarios one by one but don't know how to change select attribute runtime.

e.g.
In my first iteration select attribute is "customer" it works but in next iteration I want two attribute in select attribute "Customer" and "Beneficiary"

Please do needful