Factorio supports changing the game properties and logic via modding in Lua . The community has created quite a lot of interesting stuff already.
The official place for hosting, browsing and downloading mods is the Factorio mod portal . You can also browse the portal from in game from version 0.13 and greater.
Check out the wiki tutorial on installing the mods you have chosen.
Again the best resource of information is the forum and wiki. Check out the general introduction to modding at wiki. But beware, it is a bit outdated.
Starting with 0.12 there is also an up to date reference documentation of the modding api . This is generated directly from the Factorio codebase.