so the passenger side mirror broke off :/

Can i use an S4 mirror for an S5 car? Not sure if there were any tweaks

 

Your car will look funny as the styles changed between the s4 and s5 Aero-style mirrors.
The s5 looking more aeo-dynamic than that of the squareish aero s4's.
They will fit and work the same on either car but if you want it to look right,get both mirrors.

 

I have a pair of s5 aero mirrors cheap due to a small chip in one of them. It's a small crack on the passenger side. Could fix with fiberglass or cover with plastic weld/bondo. Let me know