When GiveNow creates a campaign in Salesforce, it updates the cause Salesforce Campaign ID field. GiveNow uses this field first to look up the campaign in Salesforce. This way, changing the campaign name does not affect receiving the donations.
Note that the Salesforce Campaign ID cannot be modified in GiveNow. If you would like to send the donations to a different campaign, you will need to change the Salesforce Campaign Name on the cause.