In the case you may need to change prices on something (memberships, store items, discounts, or taxes), here's how you can do that...
Memberships
When you change the price on a membership, it won't affect a membership that is already assigned. You'd receive this message when changing the membership price:
There is also a case where you may have multiple payment plans on the same billing cycle.
Example: $205 every 4 weeks and $180 every 4 weeks
You would have to go into the membership area of those members and click 'Change Price'.
Price changed in membership set-up: click 'Apply Price'
Something to be mindful of is a Recurring Fee you may or may not have set-up with the initial membership. If you set a recurring fee on the $180 price, it will carry over to the $205, whether or not it's set-up in the Payment Plan or not, and vice-versa.
Taxes
Same goes for taxes, except you can't change/edit the tax rate in 'Billing Set-up'. You can create a new tax rate and reassign a new tax rate to the memberships.
Discounts
You can manage discounts on memberships the same way you edit the tax rate: click 'Manage Discounts'
You'll be able to remove any current discounts, select a different coupon, or create a new coupon.
Store Items
Store items are one-off purchases and can easily be edited/changed, including adding or removing new tax rates and adding or removing discounts/coupons.