My understanding is that those parts can in fact convert a semi auto to full auto. It is true that the Tech Branch would certainly take notice of any full auto fire control parts in a semi auto. If a full auto selector with the other full auto fire control parts are in an unmodified semi auto AR receiver, even if the upper receiver has a semi auto carrier, the Tech Branch would consider that AR-15 an unregistered machinegun. If the selector is placed in the "AUTO" position, that will push the disconnector out of the way. Without the function of the disconnector, the hammer would follow the carrier back into battery. That could create a "slam fire" condition. Depending on the sensitivity of the primers, the next round could go off. If it did that would meet the definition of machinegun. This would not make reliable full auto function, but if the Tech Branch can make the gun "slam fire" once, is all it takes to be an unregistered machinegun.
The same could happen to a roller lock full auto trigger pack that was improperly converted for a semi auto application. To modify a full auto pack for semi auto use the section of the trigger frame which has the hole for the pin the "catch" (HK term for auto sear) rotates on, must be removed from the trigger frame. A new hole must be drilled through the frame to mount the trigger return spring in the pack. Another step is to relocate the trigger stop permanently in the pack.
The full auto stop allows the trigger to be pulled back far enough to eliminate the disconnector feature. So as with the AR with the full auto trigger, disconnector and selector, if the semi auto trigger group, without the semi auto trigger stop installed, and the selector is placed in the "AUTO" position, there is nothing to stop the hammer from following the carrier back into battery. This could cause a "slam fire" condition occur. The semi auto trigger stop doesn't let the trigger go back far enough to eliminate the disconnector feature. So both those modifications, plus the notch in the full auto hammer that would be used by the "catch" must be removed. All these modifications must be done to properly convert a full auto roller locked trigger pack for semi auto use.
My intent was not to insult you. My understanding of the AR system is with those full auto fire control parts in a semi auto AR, that semi would be considered a unregistered machinegun. To my knowledge you were posting misinformation. I have misunderstood different aspects before. We all make mistakes. I'm not saying that I'm an expert. I do own both systems and paid quite a bit of money for them. To set up both systems, I've spent quite a bit of time learning how those systems work. I would think very few users of this site are looking to illegally convert a semi gun to a machinegun. I'd think many more would get into trouble trying to convert a full auto pack to semi pack. All the modifications listed above must be done to avoid a "slam fire" condition, or to have a pack that would not be easily converted. YMMV.
Scott