Yes. You can edit both the usage terms (credit type, membership type) and the payment terms (packages and contracts).
Editing Membership Contracts or Credit Packages
Any changes made to a credit package or membership contract will not impact sales that have occurred. If you change the price, only future sales will have the updated price.
If you change the name of a contract or package, the new name will be reflected on past and future sales. It is recommended that if you wish to change the name of the membership contract, you create an entirely new contract.
Editing Membership/Credit Types
Once a membership has been created and sold, any changes made at the Membership Type level will apply to those who have already purchased the membership as well as those who purchased after the edits were saved.
Guest Allowance
If you change a Membership Type from Members Only to Members and Guests, you must immediately edit the Membership Contract(s) to specify the number of guest usages per payment interval, as it will default to Unlimited.
Penalty Fees
If penalty fees are enabled while editing and the membership has been sold to customers already, no-show and late cancellation fees will be charged for each penalized reservation.