[fel64]

Ah, whooami. She’s a pleasant one. What she probably meant is, you could not use wp_register() and do your own new function in your theme that does what you want; that’s probably a better solution than changing core code. It’s easy; you could just copy all of wp_register() into your theme (everything from function wp_register() { to the final }, change its name and then make the changes you want, and use that instead. Probably worthwhile, too.

There’s a very easy way! WordPress sets $id to be the user ID. It should be available, so just try it. If it’s not, you will need to put global: $id; in the line of code above it, so it knows you mean the global variable $id and not a new one.