An unspoken rule of Custom Decors I have learned of recently, is that every art you use for a custom decor is limited to be used 20 times only. Any further use of that art will be rejected. "To avoid there being 100 recolors of the same thing", as reasoning.

I personally feel this unspoken rule is unreasonable and needs to be lifted.
My arguments:

1) Each custom decor, new lineart or old, takes the same server space and costs exactly the same 10 GB to create. There's no difference if it's new art or old in that matter.
2) It cannot be abused as it still costs 10 GB per each custom decor you create. Only if you spend GB you can have that many. 20 decors is 200 GB, if someone is willing to spend over 100$ on having many recolors of same lineart - I feel it is their right to do so.
3) That limit is heavily capping the users' availability to enjoy custom decors. It is up to the user if they want so many recolors of a single art, or different ones. (example: Uniformity. I want to have a pride made into a Hyena Clan, and I can do that with overlay custom decors, BUT not if they're limited to 20 per art. They will loose uniformity once they reach the cap; I would be forced to use different art beyond that limit.)
4) Custom decor art is already limited and heavily moderated by quality and content; it is hard and expensive to find artists willing to do arts of custom decor accepted quality, and this rule limits the way the user may use their hard and expensive commisioned art. Given the fact most custom decor artists only take real $ commissions to make it, I find it unfair to limit person's use of that hard-earned art to only 20 times.
5) And of course, "to avoid 100 of the same thing" is very subjective, it is NOT a bad thing to have many recolors of one thing just because one person doesnt like that. Others might, and others would. Someone likes realistic style, others more stylised, some prefer hard-edged lines, others like it smooth and blurred, some users scroll past human items on lions with dislike, others buy and enjoy them - everyone's different. People's pride stories and roleplays may depend on their characters represented in their lions through custom decors, and that limit on having a uniform art for them all is killing the fun for them.
SOLUTION: A solution for users that dont want to see many recolors, could be adding a new tab in Custom Decor Submission called "Recolor?" that users fill in Yes or No upon submitting the decor, and a tick box "Hide Recolors?" in custom decor search. If the tick box is checked, it will then hide all decors marked as Recolor from search. Sweet, simple, everyone's happy?
6) And last but not least... demand is very important to consider. Nobody will bother creating 80 recolors of something nobody wants - IF there's demand for that many recolors, that means this decor is that high in demand, it means people WANT there to be many recolors!

Overall:
This rule reminds me of a market censorship, when you're only allowed to buy certain amount of something to "not have too many of it".
Say you like a, well, a plush of a certain brand.
You buy 20 different plushies of that brand, collect and cherish them. They may look similar but it's your favorite brand, you enjoy them, so you want more.
But when you come back to the market, the seller refuses to sell you more.

"You already bought 20 plushies of that brand! You cant buy any more!"
"But I like that brand more than others," you say.
"It doesnt matter what you like. You had too many of that brand. Buy a barbie doll or a toy car instead."

That is the feeling Im getting from this rule, in a nutshell. Whether I want to spend my custom decor stone on a new art or on a recolor of an old art... should be a metter that I, the Custom Decor Creator, decide - as long as this art conforms to other rules and was accepted at least once. If I like my fav brand plushies more than other ones. After all I still pay the same money as I would for the other item; so why should be set strictly to be censored what I get, if the seller still gets their money?

POSSIBLE ALTERNATE SOLUTIONS:

Raise the Limit: 20 is a drastically small number; it may sound reasonable for things like glasses or hats, but what about more generic and popular themes, like a hyena, a wolf, a lion itself after all? Something a lot of people want recolors of? 20 is very little when the theme is highly in demand and many people want recolors of that art for themselves, of their characters/lions.

So either raise the limit to 50 or more;

OR make the limit account-based! 20 recolors per art PER ACCOUNT, so each user would be able to have 40 submitted decors across their two accounts, AND other people would be able to have some too should demand for that decor be that high the 40 already submitted recolors cannot satisfy it!

OR make the limit time-based. So say no more than X recolors of single lineart per month, but overall total is unlimited; so the users who have recolors can just wait and submit their recolors later should there be enough demand for many of them. It would space them between submitted decors but still allow more to be made eventually.