When you double click the file, you can set whatever editor you like.
If you want an editor to start when you finish postprocessing, that can be done at the end of the post. There are samples sround - check the NX post library or nx.cam forum.
I am curious - why do you need to edit the posted output?
I dont need to edit output. I want to send it to the FTP site and add it in CIMCOEdit NC base. That is why i need external program - just to speed things up.
Can this be done in Postbuilder? How? I didnt find any settings like this. Should it be coded in TCL?
You could consider to copy it to the ftp server from the postprocessor or execute an external command from within the postprocessor. Executing an external command is not as stable as a copy/rename. If the user waits too long or clicks a bit too fast the whole nx session will stall.