safe to switch newly cycled 10g to 20g?

All my water chem readings indicate my tank has finished cycling. I've read many places to do at least an 80% water change at this point.

I just got my hands on a brand new 20g tank for $5 and I know patience is the name of the game with saltwater tanks, but since I've only got one filter and everything in my 10g is cycled, can I just put my existing water, filter, LR, sand, and coral banded shrimp in the 20g and add water of same salinity and temp to top the tank off?

Or am I just asking for trouble? How can I go about this as safely as possible??

Should have included this...sorry...

temp=80.8F
pH=8.1
NH3=0
NO2-=0
NO3-=20 mg/l

10g with penguin 200 filter, good flow, instant ocean salt, aragonite substrate, 6lb LR, one newly molted coral banded shrimp