And why exactly do you want that? But anyways it's not possible as for now.
You can use notepad++ instead if you want for auto completion or different syntax highlighting, useful info on how to do it with notepad++ is available here : https://sampforum.blast.hk/showthread.php?tid=174046
Make your own "Makefile Project". Specify the pawn compiler in the build/rebuild commands. Or rather edit the makefile by yourself. Still not sure if that would even work. Stick to Pawno, or rather use something like Notepad++ or Sublime Text.