Inaccessible head seacock shoudn't be.
I've seen toilets overflow underway because the head intake seacock was left open. (Yes, I KNOW the dry/flush valve should prevent that, but dry/flush valves are highly failure prone) Since moving the thru-hull is a bit impractical, install a vented loop in the head intake between the pump and the bowl, and as a backup, install a shutoff valve in the line between the thru-hull and the pump that's accessible to the user...if your toilet is plumbed to go overboard at sea, install another one in the head discharge line unless the discharge seacock is accessible. And keep both closed while underway--in fact, it's better to keep 'em closed at all times--except when the head is in use.