Can you change just the u-joints on a 2000 CR-V or do have to replace whole drive shaft?

You can replace just the U-joints on a 2000 CR-V driveshaft. However, it's a more involved process than simply bolting on new joints. It requires specialized tools to properly remove and install the U-joints, and you'll need to carefully press the old joints out and the new ones in. If you're not experienced with this type of repair, it's best to have a professional mechanic do it. Replacing just the U-joints is generally cheaper than replacing the entire driveshaft, but the labor cost might eat into those savings if you're paying someone else to do it.