You can always go back and unblock friends, but keep in mind they will then be able to send you Snaps, Chats, and view your Stories and Charms.
To unblock a friend…
- Tap your profile icon in the top of the screen
- Tap ⚙️ to open Settings
- Scroll down and tap 'Blocked'
- Tap ✖️ next to a name to unblock that Snapchatter