If you're taking out a residential fridge and putting in another, yes, it's as simple as taking out one and putting in the other. Now if you're swapping out the Norcold or Demetic with a residential fridge then yes, you need to do other stuff. To help you better please provide a little more info..
1. Model of fridge you want to remove.
2. Model of fridge you want to replace it with.
Most folks replace the Norcold 1200 with the Samsung 197. There's tons of info on that swap, here, youtube and other sites.
The RV tech is correct in what he's telling you, sort of... If you only camp with electrical hookups, then you won't need additional batteries.....Dennis