from what I've seen in the last couple of years clearance items are all final sale. Yoox usually rotates the clearance section twice a year to move the off-season items off of the main sale section and also serve the purpose of price retention. When Yoox begins winter sales later this year many items in clearance will be moved back and become returnable.
Another tip relevant in the US: Jet.com has access to certain inventory on Yoox. Right now it reflects the clearance section. Coupons on Jet.com are applicable to all these clearance items, plus if you opt for waive return you get additional discount. It's standard Yoox package with return label. So I suppose if you order from jet.com you can return them and depending on whether you chose to waive return you might pay a small fee.
Interesting, so items are constantly moved in and out of clearance. I wonder how many seasons old the item I'm looking at is. It's too bad about the final sale policy, there are quite a few items I like but unwilling to buy due to sizing concerns. I'll take a look at jet.com but I'm in Canada so I don't know if I can use it.
Do clearance items ever get further markdowns, or only 20% off codes?