I think that you can do this with the existing artificer class. Tell players that they must tell you how their abilities work without magic before they can elect to use them. However, I think the reskinning will be evident unless the player is a very good storyteller.
In terms of pure realistic technology you run into a problem - mass production. If you make a gun, why not make 100? You don't really naturally end up with a Tony Stark when you have people that can create amazing technology. You end up with rich people that own the IP who enjoy their laurels and a lot of people giving away their money to use the IP. That is a less heroic tale.
I've approached this problem in a different way in my world. Rather than looking at technology as an alternative to magic, I use technology as an interpretation of magic.
There are five types of magic in my setting: Psionic, Arcane, Divine, Natural - and Elemental/Supernatural (unfortunate names that have been there a long time, but that cross over into other spaces in the game that do not directly relate) .
That last type operates distinctly differently than the other types as it does not power spells. Instead, it is the magic behind spirits, behind supernatural abilities - and behind science. When a bomb explodes, a scholar will tell you it is a product of the elemental magic that suffuses the universe being invokes through chemical reactions.
With this in mind, I have beings that use technology. There are even places with technology that exceeds early 21st century technology. However, their diction is suffused with magical terminology, and the limitations of my world make mass production of anything very technologically intricate very hard as the magical weave through which the arcane, divine, and natural magics flow tends to wreck havoc with chemical reactions and electrical operations. So, those that have developed societies based upon technology tend to be isolated in places with little to no access to 'traditional' magics.
I have a technologist class that has four subclasses: Engineer, Chemist, Physicist, and Biologist. It is an NPC class so far (one player expressed an interest but backed off when I explained the limitations) as it is not terribly combat oriented, but it fits into the lore of my world. Where they do have combat abilities, they use their forte to change the battlefield or alter their foes/allies. Engineers can cause controlled collapses of natural terrain, operate vehicles with weapons on them, etc.. Chemists can mix chemicals together to cause reactions that can do a variety of things. Physicists have skills at utilizing mass, velocity, etc... at lower level, but their higher level abilities are based upon theoretical physics ideas. Biologists get bonuses to damage that are based upon how much they hit by, as well as capabilities to generate or mimic natural compounds like poisons, acids, etc... They can also build apparatuses that mimic the natural capabilities of creatures (natural and fictional). None of them is going to win an award for their combat capabilities, but they've been able to adventure alongside PCs as NPCs without issue.
