I’m on PC and I got a wardrobe in the Archmage room which I use to store all the items I don’t want to use, but want to sell. I am now rich enough to forget about those items (100K gold) and I want to remove them so that they stop bloating my savegame. Is there any way to reset the content of that wardrobe to zero with the console or otherwise, while not transforming that non-respawnable wardrobe into a respawnable wardrobe ? (I just want to reset it once, I do not want it to start reseting itself every 30 days).

Why not just sell thm? The whole thing could take about 5 minutes.

Or take everything, go to nearest house in town (not one you usually visit), drop everything (on the floor or in a respawning container like a sack) and stay away until the house has respawned.

Be careful what you get rid of though, so you don't lose dragon priest masks or such.

Yes selling them also level you speech skill even if merchant has no gold left.

For dumping them, I would simply kill some random bandit or animal and put the stuff on them as they disappear far faster than containers reset.

True, that's a simpler solution than mine.