Collage is a recognized form of art. And that’s what you’re describing.

There’s lines where you might run into issues, particularly if you’re using significant portions of single images, or the overall image hews to close to one.

But, from an artistic standpoint, it’s your own work. You’re creating something out of pieces, materials. That those materials existed as complete works of art before being separated isn’t important for that, imo. It’s artistically no different than using shells or pine needles or rocks to create a new image.

Not that you wouldn’t run into people saying otherwise. Hell, you could be Matisse and you’d have someone saying “that ain’t art, my kid could do that”.

Back in my college days, I took a few art classes. One of the projects was based roughly on what you’re asking about. We used multiple references, cut up, to form a single reference. As a lesson, the goal was to break loose from rigid thinking, and learn to be transformative in creative ways. As art, a thing made by a human to communicate something to other humans in some way, it doesn’t matter what your materials are, it matters that you make the attempt.

Now, for your basic idea of designing a fursona, it’s brilliant. Simple, easy enough, but still conveying your goal. You might see debate over whether that’s art, or just design (they can be the same thing, but don’t have to be), but it’s a great way to get what you wanted. Would a different head pasted on only your body be transformative enough to be interesting? Nah, not to anyone else, but it’s still a cool idea for building a fursona.