Hull restoration in its current version has two problems:
1) In a standard fleet/playthrough it can seem very strong, because of possible millions of credits you save with just the automatic D-mod removal. Thus players may think they have to put their first 5 skill-points into industry, which limits their skill options overall.
2) On the other hand, for a scavenger-playthrough it isn't really useful, mainly because it's a tier 4 skill. You get the most experience to unlock skills through battles, but you first need a fleet to fight them and so: No fleet, no experience, no new skills.
So here is my suggestion:
1. Remove "Chance to remove one d-mod per month from a randomly selected ship in your fleet" and "Chance to quickly remove one d-mod from newly acquired ships; higher for ships with more d-mods" from HR.
Instead HR could get a new effect tied to s-mods build in hull, like improvement to after battle-repairs/cr-recovery or reduction to supply/fuel consumption or something combat related like bonus to ECM/reduced cr-loss/somethin differen (feel free to make an own suggestion).
The theme here is: "Support of a high-class fleet which already has a lot of s-mods", in opposition to Derelict Operations which supports a fleet with a lot of d-mods.
2. Add the new Tier 1 skill "Non-certified workshop" (or "Way of the outcast", but that sounds a bit edgy).
It could either fit in the Industry- or the Technology-tree.
This skill gets the two effects:
- Chance to remove one d-mod per month from a randomly selected ship in your fleet
- Chance to quickly remove one d-mod from newly acquired ships; higher for ships with more d-mods
But to counter it being Tier 1 and not make it a new must-have-skill, it gets also two negative ones:
- Increase the price of ships on the markets by 100 %
- Reduce the amount of credits you get for selling ships at a market by 50 %
With those two effects, the new skill still remains very useful if you refurbish ships for your own use, but it also doesn't turn into a "shortcut for quick money". Plus, you get the option to use capture ships from the beginning of the game, in exchange for buying ships being no longer an economical sensible option.
Also at Tier 1 it still has some strong competition with the other Tier 1-skills from Industry and Technology, which are also very useful for an independent player.
(Another idea would be, to add those effects to the existing salvaging-skill, but also salvaging has in its current state its own, different use.)