Yes, you can. No config will be lost.
But keep in mind to bring the new switch online (stand alone) to get its firmware update before.
Meraki´s recommendation is to power off both switches before connecting the stacking cables.
As we did the same a couple of weeks ago it works without powering off the productive switch as well.
After all is connected and online (first only with 1 Uplink (recommendation Meraki as well)) switches will appear as potential stack.