Can I edit a membership plan after creating it?

Yes. Go to Account Settings > Memberships and click Edit next to the plan. Changes such as benefits, limits, events, terms and image can be made at any time. If you increase the free tickets per period, current members receive the extra tickets straight away. The one exception: once a plan has current members, it can't switch between auto-renewing billing (3 years or less) and paid-once billing (over 3 years, or lifetime). Create a new plan for that instead.