If the design is original, it is copyright protected and you should not copy it. However, most quilt designs are not original. In most cases (but not all) the copyright applies to the pattern instructions and illustrations, not to the quilt design itself. If the quilt is made up of blocks in the public domain (and most blocks are), you can copy the quilt without any problem. An applique design is more likely to be original and protected by copyright. Patents don't apply to quilt patterns.
Cashs mom - the copyright police may not have shown up - yet - but Disney is very serious about prosecuting people who copy their images. That is their intellectual property, and they make serious money from it, so they protect it.
Whether you change something a little, or whether you sell it, or whether you show it, has no bearing on whether you're copying someone else's work without permission. You will probably never be caught, but you will still be cheating. Even if you purchase a pattern, you still technically need the copyright holder's permission to show a quilt made from that pattern in a show. (Permission is almost always given.)