Otherwise, this kind of mod is easy to build
It would be if there were events in includes/ucp_remind which there aren't.
Further it looks like user remind will stop at the first finding of a users email address. If it is allowed for the email address to be used more than once the query will choose the first one it runs into which may or may not be the user that is requesting the email.
Not really sure how that mod got validated given that one can ignore the username part of the request.