I read somewhere once upon a time that if you had the TFC only version of HL you could rename the .exe to HL.exe so as to allow you to play the mod version of CS. I do not own blueshift so I dont know what the main .exe file is named or what the directory structure is, but if it deviates to much from the original HL then I suspect you would have to do some work there. Also with all the recent updates to HL I wouldnt know how that would leave Blue Shift in relation to compatability with the current game version.