Well, I've managed to replicate the "exploit" to
some extent, but then I got bored (and, frankly, ran out of resources, also I need to get to the hospital early to get my stitches removed, sooo...)
If anyone cares enough to check the possibilities, here's how it's done:
1. Craft a kebab, using spices. Or any bread/pie/pastry allowing to use spices. "Pitbaked goods" work too, although they take more time.
2. Burn down whatever you've crafted. Repeat 'til you get a decent amount of Spiced-up Ashes.
3. Craft a gildable item that uses Ashes in the recipe. I personally went with Ashen Robes, I guess Hirdsman cape would work too (and prolly be a better choice, see below). Altough you can make Spiced-up Black pigment, the sketch doesn't retain any properties (and here was I, hoping to get meself a shield made of 100% chicken!).
4. Now you're a proud owner of Spiced-up gildable item. Gild it with a bear tooth, lynx or wolf claw.
5. Repeat steps 3 and 4 for more Spiced-up items gilded with bones. When you feel lucky - recycle them. An Ashen robe with a Bear claw has a very low chance of recycling, hence - hirdsman cape would be better.
6. If you've managed to "poke out" some bone gildings - those now have the same Spiced-up properties.

Burn them in a kiln, get bone ash, make bone clay. That's how far i've gotten.
Interesting fact: bone clay retain ONLY the Spice properties, no meat whatsoever (I was mildly disappointed because of the hilarious amount of various bollocks i've included in the whole "exploiting" process).
I've managed to get 3 pieces of clay with Dill (5%), (7%) and (10%). Unsurprisingly, when used with plain and simple ball clay, they've returned a non-spiced unfired treeplanters pots (I think the percentage got below the minimum threshold and the property got dropped, but I'm not going to waste all my Fine Clay stash trying to replicate that again). I wouldn't expect a Kiln or a Potter's Wheel to even have the capability of being "Spiced-Up", so, imo, best bet is to make Treeplanter's Pots and see where it gets you.
Oh, yes, and bone saw deserves a check-up as well, although I fail to see what can a spiced-up board be used for... Spiced-up bucket?
Have fun, and if you succeed - be public about it. Remember: loftar loves people who replicate bugs, allowing to fix them!