I want to create a membership type that is non-renewable. Let's say a membership that lasts for 6 months and is free.
If someone is already a member and clicks Join again (which is effectively a renewal) then I do not want them to be able to extend their membership (in other words an extra 6 months free). Is this possible?
I don't think non-renewable memberships are possible at the moment. Your options are to play with CiviDiscount and/or CiviRules.
You could offer a discount to get the first period free, or as petednz suggested look at negative discounts. I think the negative discount (fixed amount not %age) will need to be applied to existing members.
You could also have people add them selves to a group (say Trial), which gives the same privileges that the membership would provide, then perhaps CiviRules could be used to change the group to another say Trial expired, after 6 months.
I revised what I did here. Instead I used a Drupal rule to check the contribution path when someone renews, and then used the API to check if an existing trial membership had ever existed. I then executed some jQuery to hide the first row (the free trial) on the membership signup price set. This has the advantage of retaining membership upsell.
I would look at CiviDiscount and see if it can let you provide a negative discount for the membership and make it only available to people who have no Membership Status or similar.
