Hi,
I would say FORMER_CEO is a better approach as that is more descriptive and it would make the Cypher query a little bit easier to write and more readable to others. I can't remember where exactly but I watched a tutorial either on the Neo4j YouTube channel or on the Neo4j Graph Academy with a similar scenario. If you proceed with the general CEO relationship that wouldn't be too bad either, but then you'd have to use a WHERE clause to look up the former role property and that may slow down your query.
And as far as updating your graph database, I'm also at a point too where I need to come up with a way to update my graph database on a periodic basis with fresh data. Deleting and creating a new graph database is just not scalable for us. Maybe this thread will be relevant to you once you get to that point:
Additionally, I learned that Neo4j is in the process of replacing Kettle with Apache Hop as the project management tool so you can give that a shot as well:
On-Demand Webinar
Analyzing Data Orchestration Lineage with Neo4j
Best of luck!
-Tony