Thanks Jerry !!
I think that will work for me, I will test it later, but this looks like the solution I searched for 
I have not tested it yet, but I think, it will only work for the output of the XML file, or? If it should work for both (output/input of xml <=> itab), with same Transformation, the method "GET_NEW_DATE" should be extended a bit
But this sould be possible without problems.
best regards,
Christoph