Ok next question, is it possible to expose the External ID field on Locations for editing?

No it's not and that's intentional. External ID is a primary key on all the tables it exists I'm pretty sure. It's really meant to be the primary key from another system you may be integrating with, so it shouldn't be easy to change. If your company isn't using it for that purpose, you should probably just spin up a custom field to hold whatever information is currently in there.

I agree that it should not be editable for end users, but I find it frustrating as an administrator that it's not possible to natively display or edit the externalid directly in the UI. We have some records where we need to see the externalid so we've added a custom field that is a formula field showing the externalid.

We are using it for integration with Salesforce, but they get out of sync occasionally (there isn't an integration specifically for locations). It's just one of those "magic button" requests where the user thinks it should be doable / best practice when it's not.

External find can be exposed but it is one-time editable when its is created. Once the record has been created, you wont be able to update the external id. If you need more context, please DM and happy to help!