Most people don't use cursed items. At least I've seen almonst none, wearing cursed items. Here's what came to my mind: Let some NPC sell a "wand of uncursing". This should be expensive. I.e. 1 million. This would be a single use item. If you use it on a cursed item, the wand would go poof und the targeted item will become uncursed. Therfore the property "Cursed" should be replaced by "Uncursed". And also if it had no durability, i.e. jewelry, it would get a durability 255/255. Furthermore it should become brittle, so you can't use the item forever and has an approximate lifetime as an imbued item. Now here comes the catch: If you repair an uncursed item, the item will become CURSED AGAIN! If it's insured or blessed, that will be removed as well. Thus, if you want to uncurse it again, you have to buy another wand. Here's another idea for a "Cannot be repaired"-Item: Let some NPC sell a "wand of fortification". Again this would cost some gold, i.e. 1 million. Single-use of course. To use such a wand, the targeted item must have the "cannot be repaired"-property and has to be in perfect condition (= the durability has to match the maximum durability). So if you use it, the property "cannot be repaired" will stay, but the durability would be increased to 255/255. The "perfect condition"-constraint would ensure, that you cannot wear the item down to almost zero durability then repair it up to 255 as well as use another wand a second time on that item.