To whom the assets are left to In the Trust has nothing to do with the legality of said Trust in Reguards to aquasition of NFA items at this time. Assets held within the Trust have nothing to do with legality of said Trust within NFA. ATF does not get a list of ascets. They know what you have NFA wise.
Amend it, don't amend it. ATF has no clue. They only know that at the time the paper work was submitted it was a legally recognized Trust within whatever state you reside. You could make 100 changes over the course of your lifetime after the acquisition of NFA item. ATF would never know about it unless you filed to make or register another NFA item and sent them an amended version.
Should you amend it ? Yes, probably. It only matters for others access to items now and your wishes when dead.
And makes the transfer after your death a little easier. Maybe... You won't care.
Changes in July bascily kill the need for a NFA Trust. Might as well just get what you want as individual. Your heirs can still get those items transferred. They would be personal ascets lumped in with everything else and go through probate and then ATF.