First you need to connect to the Exchange server and AD.
Then select Custom Bulk operation.
Then click add and select Other folder properties. This process needs repeating for system folders too.
Select Modify and in the property drop-down find PR_REPLICATION_MESSAGE_PRIORITY and enter the value 1
Next click OK
PFDAVadmin works through the database altering the values. This can take some time if you have lots of folders.
When we inspect the setting on any of the folders you can see the Replication message priority has been altered.