When I finish my trial and sign on to a paid account, will all of the changes and customizations I made to my trial account be lost?
Don't worry! All of the customizations and changes you have already made in your trial will stay with you when you move to a paid account. This applies to everything from custom triggers you created to the talk number that is associated with your account.
If you do NOT want the customizations you made on the trial to transfer over, simply create a new trial and turn into a paid account right away. See how to do that in this article: How do I upgrade my trial to a paid account? To keep the same subdomain in your new trial, follow the directions in this article: Can I get my old subdomain back?
If you want to keep your customizations but start fresh with none of your test tickets, you can follow the directions in this article to bulk delete the tickets in your trial account: Bulk deleting tickets.