Downsizing temporary drive

I have a 1.5 TB drive that has increasing reallocated sector count and is under warranty. I was going to pull the drive from the ReadyNAS NV and send it in to the manufacturer. I was wondering if I can put a 2TB drive to replace the unit to have a redundant system and then when I get the replacement unit back from the manufacturer, put back the 1.5TB in place of the 2TB drive.

Current Setup:
ReadyNAS NV
4x1.5 TB
X-RAID

Thanks in advanced.