Antryg,
you have the following possibilities:
- ask Gods for BLUN25 and throw away BLUN12.
- ask Gods for MISC5K.
Going into the house for MISC5K without the quest will not work - you must have the quest. Otherwise, MISC5K isn't there.
Killing Sarles should not work. I've never tried it but I tried to give MISC5K to him and then pickpocket him. I supposed that I would be able to complete the temple quest in the "best way" and that I would gain BLUN25 still. No, MISC5K wasn't in his inventory. Thus, I think that MISC5K won't be dropped by him after the murder.

I can assure you it does work. The items which can be pick-pocketed are not always the only ones which are carried. When he is killed he says, "No, my work, it isn't finished..." and drops the real stuff.

Where do I find the mace of disruption?

in a blood pool in bhodi's lair