Question about mapmaking and mods.

I'm interested in the following: I've played some maps that had mods embedded in them. How can this be implemented? P.S. I'm interested in how to replace hero models in this way, for example, replacing the Biara model with the Seraphim model. Experienced modders, please help, I'm very interested in this topic. If this has already been discussed somewhere, could you provide a link?