default WordPress welcome email not changing

I have been trying to edit the new user welcome email for 5 hours now and no matter what I do, the old boring email that gets sent gets sent. I have tried 3 separate plugins and I even tried editing the pluggable.php file by adding the word “Your” in front of username so I’d know I was editing the right line; and it still sends the original email. I don’t know how that’s even possible.

Using Theme My Login
Using PaidMembershipPro
Using WooCommerce
Using Chimy User Manager

All plugins are up-to-date.

I don’t know that this ever worked before 4.0 because it’s a brand new site that was built on 3.9 then upgraded to 4.0 then launched.

Any help is appreciated as I need to import 485 members and send them a specific welcome email!

Thanks!