Handheld GPS questions

Hey - I currently have South America on my handheld device, the image is around 4gb. I’m looking to add former USSR countries and I have a few questions

I was told by someone who wasn’t sure, that my garmin (oregon 450) could only read fat32. Is that true? If it’s not, I could reformat my SD card and join the new countries onto those I have. If it’s not, I’d need to make a new, smaller image without the countries I already have.

Question #2 - would I lose my waypoints doing this? I assume not, because its not writing to the image, so if I add a new one on, it just remembers the coordinates.