would you be able to make a content pack for a kill everyone contract in every map?

I'm not a fan of these contracts myself, but look at Terminator Mode on https://onionsquid.itch.io/hitman-3-content-packs: it adds a new mode focused on killing to each vanilla game location, created by kercyx

If that is not what you want, you can create your own pack: download the modder tool to get an introduction to modding with the framework and look at existing content packs for examples.