Is it possible in ArcGIS to change order of the parts in multipart geometry?
In the context menu i founded "insert before" , "insert after" but it never comes active ... or is it possible via python?
On the ArcGIS 10.1 help page entitled Using the Edit Sketch Properties window there is a note which may explain why those context menu options are disabled:
Insert Before and Insert After cannot be used when the vertex list is being sorted by selected vertices since it does not reflect the actual vertex order.
In any event, it seems like this functionality is not exposed in the ArcMap GUI, but I think you can use ArcPy to read the multipart geometry out into one array per part, rearrange the order of the arrays, and then write the geometry in that new order.
Your earlier Q&A (How to create Multipart Line in ArcPy?) looks like an excellent start to the code to do that.