Last question!

If you are ironing on an imagine to a t-shirt via transfer paper, can you iron it on over an existing image on the t-shirt?

Okay:
You buy a tshirt with a logo/image
You need a different image on it
You use iron on transfer paper to transfer said image onto said tshirt
Does it work?

If its a white shirt kind it should. Idk about the colore shirt ones.

Yeah it will stick but it may not cover the entire image, bits of the old may show through

Depends on the current logo. You are probably better off getting a plain shirt to use.