webhooksCreate is a 'pre-create' event.
The webhooksCreate event is triggered when you're in the context menu, editing the name, and other information about the webhook. It means that it is triggered before you actually create the webhook. That is why, you can't edit the webhook's name.
Conclusion
If you'd like to edit the name of a new webhook, use the webhooksUpdate event. The webhooksUpdate event is triggered each time you actually create or update a webhook, so you can edit it.
webhooksCreate is a 'pre-create' event.
The webhooksCreate event is triggered when you're in the context menu, editing the name, and other information about the webhook. It means that it is triggered before you actually create the webhook. That is why, you can't edit the webhook's name.
Conclusion
If you'd like to edit the name of a new webhook, use the webhooksUpdate event. The webhooksUpdate event is triggered each time you actually create or update a webhook, so you can edit it.