PO change rejection by approver

Hi Gurus,

We're currently in SRM 5.0 and I have 2 requirements:

1. When approver rejects the PO changes by buyer, there should be a workitem going back to buyer and buyer should be able to see rejection reason.

2. When buyer changes PO and sends approval, there should be another workitem to buyer where he can cancel the approval in case that he wants to cancel the changes.

I tested and found out that the above are not part of standard process and flow (normal is when approver rejects, the workitem immediately completes with 'rejected' status). Is there a configuration to achieve this? Or there's really a need to change copy standard workflow template and modify it?

Thanks.

Ray