It's definitely possible to make changes to the tech tree (I've seen that done in mods) such as some of those adjusting faction traits. That said I'm not sure how hard it is to change what specific techs do.

[Edit] It looks like this is possible but would take some work, (probably not a whole lot). Several of the techs when researched cause unlock effects on what items can be used in unit design and combining techs like you are saying should just require going through the code and combining those functions. That said there is also the issue of this largely being a matter of personal taste (mostly regarding which techs to combine).

If you are so inclined this might be a good mod to try to make yourself. I'd probably start with a couple of easier ones (like adding the Haunt hero to the general list of heros and before that one where all you have to do is change a few values in the right spots in the code to do something) and then give this one a try.

Here is a link to a modding tutorial from one of the devs if you are interested:
https://medias.games2gether.com/forums/Pikou/tutorial-modding.pdf

Also while it is a bit of a pain and requires some digging you can find mods you have downloaded at: /steam/steamapps/workshop/content/289130/
Unfortunately the folders corresponding to the mods there aren't by mod name but by number strings generated by steam so you kind of have to go digging until you find something you recognize. 289130 should be the folder for Endless Legends though (provided the numbering is the same between different computers which it probably is unless steam went out of their way to make that not be the case).

It's not a bad place to start by looking at how the game is coded (/EndlessLegends/Public/ has all of the game files I believe) and look at some of your favorite mods to see what the modders did and how it changed the game. This does require plenty of time though.