For all air weapons ranges there are two danger areas - the air danger area, and the land/sea danger area. The latter is the one that the byelaws apply to in the case of Tain. If you look at the OS map of the area you'll see the boundaries of this area marked - they extend out to sea east of Dornoch airstrip, but don't cover the airstrip. This is the same boundary as set out in the 1937 byelaws. It hasn't changed since then.
The air danger area - D703 - is marked on the chart as having byelaws associated with it, that prevent entry. But those are the 1937 byelaws, which only apply to the area shown in those byelaws. they don't apply to the rest of D703.
One caveat. The AIP entry refers to the byelaws as SI 1940/684. There isn't an SI ref number on the 1937 byelaws so I don't know if they're the same thing. But I'm pretty sure they are.
Looking at the operational consequences, you could still join on a right base for 28 from the Embo Lane and avoid the danger area (giving you about a half mile final). Climbouts from 10 would also be OK with a relatively early left turn out, or even a right turn out.
There's even room for a left hand circuit on 28 although it would involve a pretty tight base/final, keeping a good lookout for those artillery shells whizzing past your right ear!
Seems to me this is just the usual MoD overkill. Best bet is for Highland Aero Club/Highland Aviation to seek a meeting with RAF Tain and whoever the Army people are and sit down and agree the best procedures.
Also a good idea to get things firmly established for the future because the Tain byelaws are up for review at some point and it will be important not to let them sneak in something that will make ops at Dornoch and Easter more difficult.
NS