Anyone ever switch out the hard drive?

Lunar-Eclipse

Pull it out and plug it into a computer to see. If it's in a format your computer can read then you can probably image the contents to a larger drive. Do not modify a single file on the drive until you have a backup.

First I would suggest imaging the drive to a larger drive without resizing the partition. Test it and see if it works. Image the partition(s), don't copy files. Copying changes attributes like time/date/modification stamps.
If it works then resize the partition and test it and see if it works again.

My reasoning for the steps I suggest is that I imagine there are more than just maps on that hard drive. Probably the nav software or the entire nav system OS. I don't know how it will react to seeing a different hard drive brand/model/size (hopefully the systems isn't locked to a specific range of Nissan approved serial numbers for the hard drive). Secondly, the software may be written to have X amount of total/free space and may not use the additional space even if it's available.

Disclaimer: I am not a Nissan software engineer. I did not design the system and have no specific knowledge of how it will react to all of this. You do this at your own risk.

Good luck.