In answer to the question regarding changing a 54 inch pool to a 48 inch or lower pool, I've seen pools with floating skimmers, meaning it does not matter where your water level sits, it will always skim - as for your return - as long as it's still emptying into the pool it should be fine...
http://www.nextag.com/Vogue-FLOATING...31/prices-html
http://usaink.com/dragonfly/