This is feature that other Mongoose type plugins support, allowing modifying a mongoose object other than the default, with syntax like this:

const mongoose = require("mongoose");
const Int32 = require("mongoose-int32").loadType(mongoose);

The way that some others like this implement is a breaking change, because you have to call loadType() to select which Mongoose instance you want to attach to. If no instance is provided, the default is attached to.