Hacking K2 [blackpearl] Project .kprx File
If you don't already know, .kprx file is just an XML file. Which mean you can just open it inside Visual Studio or Notepad or any other text editor.
One occassion I find this useful is when you want to quickly do a find and replace operation on the workflow activity level custom .NET code since these code are stored as CDATA section inside the XML. A bit of caviat... make sure you know what you are doing (naturally).
Most of the time I found that drilling down into the workflow code level is just a bit too slow to do inside K2 Designer (at least on my machine), that's why I prefer to do it this way since it's way faster when I need to do mass find and replace on multiple workflow event that require me to do View Code from the context menu.