Hey, just wondering if we will be able to add add-ons in the pledge manager after the campaign has concluded? If so will the price be any different?

This may be a really stupid question, I apologise, but how do we pick which pin we end up getting? Is this sorted out when we pledge or during the post-campaign survey? I'm doing this on a mobile browser, and I don't know if I was supposed to choose when I pledged or not. Cheers!