Hi Jonathan,
I've used the same outbound flow for lots of different campaigns, that all had different contact lists. I'm assuming you are referring to the Contact List that you set under "Outbound Settings" in the Outbound Call flow.
What I've found is that you don't need to change this field, as it has no effect on the Outbound flow itself, unless you are planning on using Contact List properties/data in the call flow. In my case, I don't need any of the contact list info to leave a VM, so I just left that field set to a test contact list I used when I originally setup the flow.
If you are planning on using contact list column data somewhere in the Outbound flow (eg leaving a different VM message based on a value in the contact record), then you would need to update the Contact List under outbound settings so the flow knows where to pull data.
Hopefully that answers your question!