My procedure would be along these lines:
- Temporarily remove the water from the 100gallon
- Carefully lift and move the 100 gallon far enough out of the way for the new tank
- Replace the water in the 100 gallon and keep system running in new location
- Begin setup of new tank, avoid any uncured rock, add new sand, add new water
- Let the new tank settle for about 24 hours
- Plumb new tank into 100 gallon viva common sump, run for a few days.
- Transfer over livestock
- Disconnect 100 gallon
- dismantle 100 gallon and apologize to your other.
The last step is key!