What do you think would happen if you “duplicated” the drive onto a 1TB hard drive. Would the file system not recognize the actual newly available larger amount of free space?
Unlikely. Though I haven't looked at the full details of the qnx6fs filesystem implementation, I believe it's similar to other filesystems that fix the size upon creation.
To add a larger drive, one would need to be able to have it formatted appropriately with data put in expected places. Assuing there's nothing in the Sequential code to limit things, I'd suspect it may be possible but one would either have access a system running QNX or support added in the Prophet X/XL OS to format/setup a new drive. The latter would be preferable, of course.