[Freeswitch-users] How to change the contact when fs sending REGISTER??

As title ,I know how to do when sending INVITE but how to do it when fs sending REGISTER?? For example , when gateway registering , the contact is gw+abcd@XXX.XXX.XXX.XXX , how to change it to *abcd@XXX.XXX.XXX.XXX??* ** *Please help* ** **