Hey @samasarin,
To overwrite plugins you can use extensions. By copying ./node_modules/strapi-plugin-users-permissions/services/User.js to ./extensions/users-permissions/services/User.js and removing all the unused functions you can modify the senConfirmationEmail.
For example you will get:
'use strict';
const crypto = require('crypto');
const { sanitizeEntity, getAbsoluteServerUrl } = require('strapi-utils');
module.exports = {
async sendConfirmationEmail(user) {
// ...
},
};
(Do note the warning in the docs about use extensions and upgrading your strapi version
)
Good luck!