Disabling changing armor could be interesting, actually.
That would mean being unable to use my enchanted gloves in battle unless I equipped them ahead of time. I would despise that.
The item really needs to be equipped to record the charge use on the item. Additional item data like charge use cost, charge storage and durability are only created when an item is equipped; this allows stacking of enchanted items if they are at perfect condition, and non-stacking of partially used items. Multiple amulets may be possible but everything else is problems.
That's unfortunate. :cryvaultboy:
Would doing this mean you'd have to find out how this information is created/computed for equipped items and apply it to the selected enchantment if necessary? In that case, I wouldn't worry about ensuring that selection is carried over in a save file if that would mean editing the format. I'd just specify no spell selected for the save.
It seems to me like you'd only first need to be able to select the item without equipping, then when you try to cast, figure out the cost and remove X amount of charge from the item. But then again you'd also need some data structure somewhere for the spell menu to read the cost.
Sorry if my needling on this subject is bothering you, my inner programmer is quite interested in the problem.
Edit: That bit about game saving should apply to any other methods too. I wouldn't worry about trying to get the selection preserved in a save, just have it ignored. It's no big deal reselecting the item when you load the game.