Geoff,
sad to hear of your eye problem and also the bouyancy glitch on your excellent model of HMS AISNE.
Unfortunately Deans destroyer hulls, or any others for that matter, being pencil slim, do not lend themselves to any superfluous topweight. (I built HMS CAVALIER from the VERULAM kit). Everything above the waterline has to be as light as possible.
Looking at your images of the hull, the boot topping is slightly above the fourth row of plating, so there is no margin of adjustment there. (One of the easier 'fixes', I use the lower edge of the fourth row of plating for my boot topping line on all three of my destroyers).
It is a great pity that you have this problem and the only way that I reckon you can solve it is to remove the extra electronics, ie the bedstead and main armament drives.
Nevertheless it would still make an excellent static model with the existing drives. The attention to detail is superb and the model is a credit to your craftsmanship.
Here's hoping for a complete cure for your irisitis and success for AISNE whatever you decide to do.