HTML notifications
Jamroom Developers
All jrCore_send_email() functions create a queue entry via the jrCore_queue_create() function.
There is an event that fires when that queue entry is created 'create_queue_entry'.
If you use your module to listen for that event, you can add in the send_as_html option at that point.
Docs: "Events and Listeners"
https://www.jamroom.net/the-jamroom-network/documentation/jamroom-developers-guide/1011/events-and-listeners
That will allow you to avoid altering the jrUser module.