The easiest (and I say that with a bit of salt) would be to add the “hack” into the content-manager controller/services since that’s what’s being called.
Downside is those are generic so you have to read the incoming request and filter out and only perform your logic modification to the specific call/model.
I’m not super familiar with our frontend (admin) parts of the code-base in terms of modification but it should be able to be done via extensions (no npm-patch needed, but could be used if you wanted).
For the controller file, most likely here: strapi/collection-types.js at master · strapi/strapi · GitHub
And service file: strapi/content-types.js at master · strapi/strapi · GitHub
Doesn’t matter where you intercept to modify the response, controller might be easier.