Patreon has added a way to edit tier prices. This is now one of two ways that users can change a tier price. The other is “unpublishing.” From their email:
Whether you’re navigating the rising costs of business or just because the value of your offering has gone up, you deserve the flexibility to change your tier prices to best meet your needs. You can now edit the price of your tiers on Patreon, even if they have active members on them.
How it works
When you update a tier price, that new price will take effect immediately for new members joining your Patreon. However, renewals for existing members will stay at the old price for a 31-day transition period.
Handling the change
Affected members will get an email when you change a tier price. However, it’s a good idea to reach out directly to explain why the price changes.
Here is some more information.