Calls fail from pstn if extension with same number exists on PBX

I know what I am doing wrong and why it does not work, but I have a legitimate reason for this scenario and I am trying to find a temporary work around.

When we activate a new user on the system who wants us to port his POTS phone number to the VoIP PBX, we need to create the extension on the system, configure the ATA, test it and then ship it to the user.

Now we have the PSTN number live on our system but the number port is not completed so all calls fail to and from this number.

Is there any way (aside from deleting the extension, and then recreating it) to disable it, change the extension number, or change the context so that calls to/from this user work until he receives his ATA and the port is completed?

Currently I create the extension and test it with the ATA.
Then I export to csv with “Bulk Handler” and delete the extension on the PBX.
That way we can call the user and he can call us from the PSTN.

Once the ATA arrives at the user I import the csv file and re-create the extension.
It’s annoying but it works.