Sounds as though you’re on the reminders settings page.
I can confirm that changing when you get reminded about a goal will have absolutely no effect on the goal’s due date.
If you email support we can adjust the goal so that the next due date is on a Friday (or you could use the ‘take a break’ feature to inject a one-day pause).
But, and this is a big one, Beeminder does not think in terms of weeks, so the deadline could drift away from Friday again for any number of reasons. (He says, completely blind to how you’ve configured it…)