I've got an edit I want to upload and use around the site, but I'm not sure if it will be accepted or not.
The pet is the Nostalgic Irion. I edited the official art to look more like one of the original Fairy Tails birds. Here's the original Taffeta Tails and here is my edit (obviously not the one I'm uploading! xD I've got the final version ready to go ^^).
The page says:
Since I've edited the pet to make it look more like the original, I'm wondering whether or not it will be acceptable? I'd like to hear from someone with more experience with this feature before going for it. First time using this! ^^;
As that stands, for what you're going for, it won't as a custom image. As an overlay done with simple CSS, it would as people do that all the time.

Sorry I don't have a better answer than that.
If you had an image done from the sketch up, it would work fine. Custom images have to basically be 85%-99% original work, like CWs.

What about this pet? They're custom, but the image is a recolour of the official chibi dillema...meaning it's not 85%-99% original work. Or am I just reading your reply wrong?
I pulled the numbers out of thin air. That would be ticket worthy, imho. I can't answer that.

No worries. :)
Think I still need some input on this though. I've been looking at some of the Spotlight winners who have uploaded custom overlays, and there are a few edits of official Subeta art. 85% original work? That doesn't sound right. Some of these accepted uploads are simple colour swaps.
Edit: Guess I took too long posting that. x) Thanks guys. Looks like my best bet might be to make a ticket and check.