You can change it out but it's going to be messy and your stock would need another tank to hang out in during the change.
Depending on the fish size draining your current SW
into a 10 gal
tank ($10 at walmart) would be fine for the day or two it takes to change it out and the sand storm to settle. If fish are more then 4" total length I'd go with a 20 gal
Your Emperor 400 filter could just be moved straight to the 10 gal
for bio-filtration since it has bio-wheels built in.
Then I'd get a clean 30 gal
trashcan to drain the rest of your water into (without siphoning the bottom) and have a couple of clean 5 gal
buckets to hold the rest.
Remove the decor and scoop out current substrate and give the tank a quick rinse and refill. I use a Mag 9.5 Pump
and 1" 20 ft vinyl hose (3/4 inside diameter) to quickly pump the water from the trashcan to the tank. Also good for premixing SW
If you don't have a PH I'd get one like a Maxi-Jet 1200 to keep the main tank flowing and within a day or two the sand will have settled down and you can add your stock back in.
48" NO light isn't enough for most corals. What kind of coral do you have?