Access policies to grant edit rights for a Change Task shared to Project?

Hi all,

we're using ProjectLink with external designers who only have rights to Project contexts. We've managed to assign from product context Change Tasks to them as well as share those and related Change Notices to the Project. However, what should be looked at to grant edit rights to the Change Task? This is required because there's need to edit Resulting Objects by the assignee.

I've tested setting Full Control to all states for the Change Task object in the particular Project in Access Policies, but still editing is not possible.

We have 11.0 M030 CPS11