TEWS response in 12.6.x and 14.x has a TEWS keyword appended to the SOAP response. In 12.5.x the format was different. The difference between both the IDM versions are given below.
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?
Unfortunately newer versions of the product have an upgraded version of TEWS response and there is no way to change this behavior. So, all 12.6.x and 14.x TEWS calls will have this newer response type and not identical to what was seen in 12.5.x. The software you have integrating with TEWS will have to be updated to accommodate this, there is no workaround from the Identity Manager side of this integration.