If BATFE recognizes a particular item as an "arm brace for a pistol" then it's a relatively safe bet at this point* that the pistol remains a pistol and not a SBR. If not, then for sure it will be regarded as a SBR with any other attachment which can be viewed as a stock. Bear in mind that the arm brace criteria is such a large grey area at this time that some folks are even spooked with the notion of placing a devoid plug in an arm brace as some regard such a thing as a re-purposing of an arm brace into a buttstock - weird.
So to answer your question YES.
*Things can change with BATFE just like what happened in March of '17 when all of a sudden arm braces are given a pass when "momentarily touching the shoulder" whereas prior to that the directive from on high was "thou shalt not touch the arm brace to the shoulder as that constitutes a SBR."
