You can change the den or patrol name at any time. Just press the Edit Patrol (or Den) link on the patrol / den page. It is located toward the bottom.
Packs:
https://help.scoutbook.scouting.org/knowledge-base/introduction-to-scoutbook-plus-for-cub-scout-packs/
Troops:
https://help.scoutbook.scouting.org/knowledge-base/introduction-to-scoutbook-plus-for-troops/