how to change mhonarc's behaviour in qp decoding

Hi together,
I would like to change mhonarc's behaviour how it decodes quoted
printable. I could use "<nodecodeheads", but i do not want to disable it
completely. I need to change the charackter mapping, because mhonarc
generates wrong german umlauts. It recognizes qp coded umlauts, but it
outputs them as umlauts coded according ibm-437. I would prefere
iso-8859-1 umlauts.

Is there a way to do that?
           <***  hk  >***