To use a different workflow template with an existing CR type is OK. You don't need a new CR type if your process changed.
MDG Rule-Based workflow template will work for your requirements. First, you need to enhance the BRF+ application to add the fields you want to check. You can use this document to learn how to do that: http://scn.sap.com/docs/DOC-14881.
Then, you need to implement a decision table that routes the workflow step according to what fields were changed. To learn more about how to fill MDG Rule-Based workflow decision tables, you can use the above link and see this one: How to Fill MDG Rule-Based Workflow Decision Tables