Cut off tubeless plug head? I use tubeless tires ranging from 30 to 40mm in width. When I puncture and the sealant doesn't cut it, I plug the hole with a Dynaplug.

On longer rides, I carry a spare tube (or two) just in case. It occurs to me that a tube inserted into a tire that already has a Dynaplug in it will instantly puncture, since it essentially inflates directly into a spearhead. Hence when I get home after plugging my tire (or, at the latest, when inserting a tube by the roadside), should I cut off the plug head on the inside so it will take a tube, or will this compromise the seal?
Yes, you should definitely cut the head out when you get back to your house, and then patch the tire.   Whether you want to install a tube, instead of continuing to run tubeless.