Disable Write Check Box in Planning Security for Measure Group

Summary:

We want to disable write check box in planning security for measure group

Content (required):

We are trying to build plan security based on measure group. For a specific role & measure group combination, we want read only access and for an another role we want to provide write access. We are trying to make use of planning seurity to achieve that. However, when we select forecast measure as entity, then Write Enabled is checked by default and greyed out. Is it possible to define read only access for a given measure based on Role? We have explored table lock and it wasn't meeting our requirement