Yes, you can install a glass door to a prefab shower. Here are the steps to do it:
• Measure area and buy appropriate size of glass door.
• Pull out old hardware from shower walls
• Use silicone sealant around jambs for watertightness.
• Install new hardware for mounting the door.
• Place in desired position and fasten securely with screws.
The installation process is simple but might require some effort depending on your setup and preference. It's advised to hire a professional if you are not sure about what needs to be done or lack necessary tools and skillset needed for this job.