Hi,
I suggest to change the object changeability in the Data Warehousing Workbench.
T/code RSA1
Go to the Transport Connection perspective
Then click on push button Object Changeability
Here you can find object type DEST (Open Hub Destination). Please change the setting by right clicking, choose Switch Changeability.
Now you will be able to activate the Open Hub Destination w/o having to open the system.
Please refer also to SAP Note 337950 - Queries (including objects) cannot be edited.
Best regards,
Sander