Email Opt-In/Out Functionality

For countries that require email opt-in consent, what is the best practice for capturing this data on the first form fill-out and not giving them the option on further form fill-outs?  For example, if I go to a form and select a country that requires an email opt-in and the field pops up, I select "Yes."  A couple days later, I go back to the website to download a different asset, and I fill another form or the same form a second time.  Basically, I don't want to give people the option to opt-out after they have previously opted-in, so I don't want that field to show up anymore.

Thanks in advance for the feedback!

Bobby