The misctool utility used by that zip file (attached to
this post) was developed by drellisdee, one of the developers for the Amon-RA recovery for the OG Evo, originally for the HTC Rezound which is a newer phone than the Evo 3D/V. I've used it to reset the mainver on my 3D, but I'm S-OFF and have no way to test it on an Evo V that is S-ON, but according to the developer it should reset the mainver as long as the phone is rooted and that should allow flashing an older RUU/hboot with S-ON. The Rezound got the wire trick very late so the users were forced to deal with S-ON for quite a while.
In this case, if the phone is unlocked again it should be possible to flash a custom recovery via fastboot and then run the zip file to reset mainver. I can't guarantee that will work but it's the only method I've heard about to try flashing an RUU with a lower mainver on an S-ON phone.
ramjet73