Here you go:
For both of you as well and others wondering, I will update the post to include the methods provided by @Wedgewood. I can confirm that it works and that you actually can make multiple directories of different modded DR's instead of instalations all together.
What i did was just make two folders named "Modded Dirt rally [RFPEv0.4 Physics]" and another folder called "Dirt Rally Original Unmodded Files".
1) Placed a FULL copy of my Vanilla files in "Dirt Rally Original Unmodded Files" in a folder just like the one in steamapps/common named "DiRT Rally".
So the directories should look like this somewhere on whatever drive on your PC:
Dirt Rally Original Unmodded Files/DiRT Rally
Modded Dirt rally [RFPEv0.4 Physics]/DiRT Rally
2) Make sure to have the "Hard Link Shell Ext" installed:
3) Do the same thing and make a copy for an instalation of DR with RFPE v0.4 Physics installed
4) Delete the "video" and "tracks" folders from your modded "DiRT Rally" folder and link those same exact folders instead from "Dirt Rally Original Unmodded Files/DiRT Rally" location.
5) Now pick whatever one you want to play (Modded or not) and just link that particular DiRT Rally Folder in your:
"Programfilesx86/Steam/steamapps/common" folder directory. (Or wherever your Steam's "common" folder is.
And presto! Easy intergration of a modded directory without install and you saved the space like solved by @Wedgewood. To Play or install the vanilla game, just link the original DiRT Rally folder from the folder you made with it: Dirt Rally Original Unmodded Files/DiRT Rally