Exchange 2010 setup opens up the necessary ports for client server communication and by default the replication port used by DAG is 64327. If you do want to change the replication port to the one of your choice for whatever reason, you can do it.
Run the command below to change the replication port, to say 64000
Set-DatabaseAvailabilityGroup -identity "dagname" -ReplicationPort 64000
Once the default replication port has been changed, make sure that you manually modify the firewall exceptions on all members of the DAG so that communication occurs through the new port. If you have your firewall disabled (not recommended), no change is necessary.