Hi! Thanks for the reply!
I believe new videogames can be born from changing the rules of existing software designed to be a videogame.
For example, DOTA (the famous MOBA) was born from heavily changing Warcraft III's rules and was later developed into a standalone software designed to feature those custom rules. Moreover, DOTA 2's rules were modified once more to create the famous Auto Chess, eventually becoming its own standalone version when they developed software that specifically played by those rules.
I also think in GTA5 roleplaying servers, or Minecraft game modes designed by users. Speedrunning and No-hit runs also feel like their very own genre, which looks to go beyond the rules imposed by the software to play in a specific way and accomplish their own objective (new rules, new objective: new game?).
Of course, you're still using that software that was designed to be a specific videogame to play in a different way. However, it still embodies the idea of the videogame being what happens when a human uses some software to play a particular game, not necessarily the intended by the creators of that software.