What word would you give to the kind of thing I do with bikes? I take a bike in and repair it. I replace parts as needed, and I don't pay any regard to keeping it in original condition. I make it work so that someone may ride it for commuting or recreation. Most of my changes are not upgrades, but sometimes they are.

When a bike leaves my "shop" it is in perfect running order and needs no other work.

What is this called?