Typically the bulbs alone can be replaced... or of course the fixture...
I'm not sure what fixtures your rig has, but I've replaced all my bulbs aside from the bulb in the microwave... and storage bins as they are rarely used.
- Interior 'pancake' lights (bulbs encased behind plastic)
- Bathroom fixture (open bulbs)
- Exterior 'porch' light
- Microwave hood light (110v)
Each took a different bulb..
Check for bulbs rated HIGHER than 12v... All my 12v replacements were rated at 12-24V. Remember the RV will put out up to 14 volts - and can overheat bulbs rated at 12v.
Typically you will have a choice of color/temperature... I went with warm white... Cool white will be 'harsher' and may have a blue tint. A matter of personal preference.
Lights run MUCH cooler - and draw only a small percentage of the previous current.