It might be worth creating a new thread to this, since this thread explicitly deals with access tags on ways.
As far as I see, the point with these booms is precisely that the access=no tag on the way is predicated upon the existence of the boom. The boom, by the way, represents also and at the same time a legal restriction.
The access wiki page already has this point:
emergency=*– category: emergency motor vehicles; e.g., ambulance, fire truck, police car. Note that emergency vehicles are generally not restricted by legal access rules. For places explicitly designated for emergency access consideremergency=designated.
That (well, either one of the tags) could be applied to the barrier-node. As I said, the highway should remain access=no, since (as the quote above from the access wiki page itself notes and as I have noted repeatedly) “emergency vehicles are generally not restricted by legal access rules.”