Help replacing username in checkout registration

-- HikaShop version -- : 4.4.1
-- Joomla version -- : 3.9.25
-- PHP version -- : 7.4

I am modifying sub_block_login_registration to replace the username field. I am trying to fill the field value with the Email address (we already use Email for login, but I realize the J! requires a unique username, so this seems to be the safest method other than possible creating a random username based on the email address like the J! Name field does in Hikashop).

Either way, I need help with the best way to manipulate the username field after the user enters the Email address on the form.

If there is a better way to omit the username field from the process, I couldn't find it. If we use Simplified Registration with/without password, the Name field isn't available, and the Name field gets populated with the left-of-@ portion of the Email address provided.

Thanks!

EDIT: javascript! ... maybe I over complicated things a bit, so I've hidden the label/field and used javascript/onchange. But is this where/how I should be doing it? It would be nice to have an option to either randomize this, or set to email, etc. and hide since we can already do something similar with the simplified registration option.

Thank you so much...I did the first one in testing, but the 2nd choice is better. I'm glad I asked.