Is it possible to edit active camaigns?

I wouldn’t typically recommend making changes to live campaigns as it can cause some unexpected sending behaviors. If you check out the doc below, you can see a bit more detail about what happens when you make changes to a live campaign, specifically when changes are made to the segment conditions:

https://customer.io/docs/campaign-changes/#if-you-change-the-underlying-configuration-of-the-campaigns-trigger-or-filter-segments
 

Changing copy will be less of an issue though - you’re way more likely to run into trouble if you change the trigger segment or filter conditions etc. You can technically make copy changes without pausing if you choose, because as I said - no configuration changes are being made that will change someone’s journey. But I’d recommend setting your message to draft just in case so you can make sure you’re not going to cause issues with links or anything while you’re working. 

You can’t pause a campaign, you can only stop it and then resume later. For that reason I would personally recommend setting the message to draft so that people will still trigger it, but the messages will queue up instead of automatically being sent. Once you’re done making your edits and confident everything is working as expected, you can release the drafts and set the message back to send automatically. This doc probably helps:

https://customer.io/docs/pause-campaign/#set-all-your-messages-to-queue-draft 

Hope that suggestion is helpful for you!