Description:
Proceed as follows:

1. Remove the relevant block in the CFC chart.
2. Switch to the SIMATIC Manager and the block folder.
3. Right-click the block and open the option "Special Object Properties > Message…".

4. Remove the "Locked" option from the message class you want to change.

5. Go back to the CFC chart and import the block via "Options > Block Types ".
6. Now you can change the message class in the CFC.

Keywords:
Message configuration