Business Change Frameworks for PMI

Does anyone have any practical examples or suggestions for lightweight business change management frameworks suitable for Post Merger Integrations?

One of the challenges I have experienced is how to effectively embed Business Change Management within integration programmes. Part of the reason for this I believe is that we have a fairly light weight programme management model to support and challenge the workstream leads to come up with and deliver the integration of their respective areas. When we then attempt apply Business Change Management it fails to get traction within the workstreams who at best just pay it lip service. Part of this is down to Business Change Managers who seek to embed a very rigid and heavy weight change management philosophy over these changes which is incompatible.

Interested in any best practices, frameworks or tools that could assist with better embedding business change in this scenario?