Sorry if this has been asked before , but can the custom songs be applied if I get Rocksmith 2014 via disc for PC on amazon.. Or do I have to get te game through steam?

Yes you can use cdlc with RS2014 no matter where you get it from.

 

Not related to the initial question, but the disc from RS 1 was just an executable with a pointer to DL from steam anyway, so it's probably the same for RS 2014

Thanks!