How to update the approver lists of an existing workflow (Request approval)

Hi,

I need to add a new approver to an existing request approval.   Really appreciate any help, hint to do that.

I tried to add members to ComputedActor of the request and approval object. I was able to update approval but not request. When try to approve, it will not generate approval response.

Another thought is to get containingworkflow of the request, update the workflow parameter from there. but not sure if that is possible?  How to trigger the workflow after the request approval already been created?

Thanks very much,

Min