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