Removed is easier...
I found removing unit was much easier. Removal takes 30 seconds. My avionics shop sold the face plate at cost. They also recommend removing the existing faceplate glue with 91% iso alcohol before attaching the new faceplate. That’s how they do it. Also, depending upon year of manufacture, some SL30/40s have little clear rectangular plastic pieces under the faceplate and below the digital display. If one or two pop out while removing and replacing the faceplate with the SL40 while still in the instrument panel... they can get lost.
Overall an easy 7 minute task including the removal/installation from aircraft.