Lock Fields in Business Process Flow

If the fields are read only in the form by default, it should also be  read-only in Business Process Flow.

but in my case, I have custom Entity 'COO'. there is one read-only Field by default. but user can edit its value through BPF manually. In ideal scenario, its value should be updated through a workflow not manual. 

that is creating conflict. 

what can be the solution for this one?