you won't be able to do this from within an xslt.
I did the following to get somewhere close to your desired behavior:
- allow the Admin role to edit incidents in Final Stae
- set a marker field (I called it aaEmailUpdate) in incident from within the xslt
- create a trigger on that field with condition Status=="Closed"
- that trigger calls a composite action which
- creates a new incident (copying some information from the closed one, adds text references, etc.); I use InsertChildObject, as I have a incident-to-incident relationship to link arbitrary incidents
- reset the marker
- Notify the owner
That way I get at least a new incident with information from the old, closed one.
However, the incoming email that triggered this procedure stays with the closed incident. There could be a way to link it to the new incident, but didn't invest any time into it.
Perhaps its a starting point for you.