There are a few scenarios that you could experience when updating guest usages associated with membership contracts:
Scenario: you sell contracts with 2 guest usages. If at a later date, you return to the membership type and set it to 'Members Only' it will not allow clients to book guests using their guest usages. If you update it back to 'Members and Guest', they can use those 2 guest usages you originally sold the contract with.
Scenario: you sell contracts with 0 guest usages. At a later date, you go in and update that contract to have 2 guest usages, those contracts sold will always keep 0 usages. Only future contacts sold will have the 2 usages.
Scenario: you sell contracts with no guest usages. At a later date, you return to the membership type, allow members and guests go to the contract, and update to 2 guest usages. Future contracts sold will have those 2 guest usages. Those that were sold with no guest usages will continue to have no guest usages.
It is possible to update guest usages on previously sold memberships but only if they were enabled for guest usages at the time of sale. Otherwise, guest usages cannot be added to previously sold memberships.
If you have sold memberships not currently configured for guest usage, they can be updated for guest usage but only if they were enabled for guest usage at the time of sale.
*Note: Changes to the membership type impact all contracts (those already sold and future purchases). Changes to the membership contract (guest usages, price, changing the type associated with the contract) only impact future contracts sold. If you make changes to the Credit Package Penalty Fee type, you have the option to impact future contracts sold or previous sold and future purchases.