TEWS calls between 12.6.x and 14.x changed drastically. In 12.5.x the format was very different. Below is only one of many examples.
Other examples include filter and subject changes.
Behavior on 12.5.x
Behavior on 12.6.x and 14.x
Is it possible to revert TEWS to the legacy version where tews: is not appended into the SOAP responses?
Occasionally newer versions of the product will include changes to our TEWS interface. There is no way to change this behavior. So, all 12.6.x TEWS calls would need to be updated in the software you have integrated with TEWS. There is no workaround from the Identity Manager side of this integration. After any upgrade, you will want to review any tews calls for functionality loss.