How to re-use message mapping for similar message structure?

Hello,

I have 2 potential source messages which differ only in the root XML node. Inside structures are identical.

I would like to use the same gui message mapping for both messages except one field I would like to switch based on the original message which came in.

So for example:

<PurchaseOrder>

<header/>

<item1/>

<item2/>

<item3/>

</PurchaseOrder>

<PurchaseOrderChange>

<header/>

<item1/>

<item2/>

<item3/>

</PurchaseOrderChange>

I would like to re-use all of the complex mappings on the header&items. Destination requires only one field to say if the PO is New or Change.

So I was thinking of using XSLT to modify root node of incoming message and make the message structure the same, but then I no longer can sense if this was a change or not!

Does anyone have an idea for how to work around this? Maybe I could set some variable on inbound adapter using module and then retrieve this in mapping.

Any experience or advice on this appreciated.

Thanks,

Aaron