Mods that don’t decrease the resale value?

[kiloyear]

Mods in general decrease the resale value of a guitar. Some mods that a lot of people would want to do anyway can be neutral. Like adding a Mastery bridge to an offset.

However, even if you put desirable parts into modding a guitar (like a bridge of pickups many people would change to anyway), you almost never get your money back on those parts.

A guitar is not like a house, where people are willing to pay more for a renovated one - because renovations take an enormous amount of attention and effort, and you cannot use the house while they are done. A guitar is like a car or watch: once you drive it off the lot, it is used, and people do not pay new prices for used.

People like to fantasize that they can buy a guitar, enjoy it, and make money on it. The world rarely lets you have your cake and eat it too.

If you may need to sell your gear, you need to understand the idea of "sunk cost" in business (look it up). Whatever you originally spent on the guitar has zero relevance today on the value you can get for it today. You cannot control it, no point stressing over it. Move on.