Although it's old news now, the ATF's changes to the regulations surrounding trusts were big news in 2016. The proposed rule was called 41P, and the now-finalized rule is 41F.
What did the rule change do? Well, it changed the CLEO (chief law enforcement officer) sign-off requirement into a mere notification requirement. This stopped local law enforcement from preventing people from obtaining NFA firearms by refusing to sign off.
The rule also created a requirement for all trustees of a trust to be fingerprinted and photographed at the time of a tax stamp application.
ATF 41P went into effect in July 2016, and none of its provisions applied to trusts or tax stamps that already existed. It only changed the rules going forward. As a result, the ATF created a "Responsible Person Questionnaire," which is a form each trustee must fill out along with obtaining fingerprints and photographs.
Bear in mind that the fingerprint and photograph requirement is only for existing trustees at the time that you apply for a tax stamp. Once you have an approved tax stamp in hand, you can add or remove trustees without triggering a requirement to submit fingerprints or photographs.