Can I turn white label off once I've switched it on?

The warning systeme.io shows before you click Activate

Directly above the Activate button, systeme.io's own article carries a warning: white label currently cannot be deleted, reset or deactivated once it has been switched on. No later article describes a way back after that point.

What happens to the domain you assign to it

Turning white label on needs a custom domain connected to the account first. Once you pick which domain white label uses, systeme.io says it becomes strictly dedicated to that feature. It picks up special routing rules and can no longer serve an ordinary sales funnel or website.

systeme.io's own advice is to set aside a domain or subdomain just for this, rather than handing over the domain your main site already runs on. Assign that one by mistake and every page depending on it stops working.

The domain can be swapped. What happens to the one it replaces is not said

White label settings do let you change which domain the feature uses later, provided the replacement is connected to the account first. What the article does not cover is what becomes of the domain you move away from: whether it returns to being an ordinary domain available for a funnel or website, or keeps the special routing regardless. Nothing published answers that either way.

Turning it off entirely has no documented route

No systeme.io article describes a support request, a downgrade or an account setting that reverses an activated white label. That is not the same as saying it can never be done under any circumstance. It means that, as published, there is nothing to click and nobody named to ask.

The word "currently" in systeme.io's own warning is the only hint this might ever change. Nothing published says it has.