You can build a “total conversion” mod.
The user would have to first purchase/install the first game (Dishonored) and then download/install your own mod on top of that.
What’s important here is that you would not copy/distribute any of the assets that came with the original game – each user has to purchase/install those separately.
using assets that already exist on the hard disk is not copyright infringement. (Although there may be some interpretations around moral rights and re-contextualization – probably don’t try to make Dishonored furry dating sims or somesuch…)