I have a question about replacing rotors. I need to replace my rear pads now, but don't have the money to do pads and rotors all the way around. I was wondering if I replace the pads now and do the rotors in the spring would I need to replace the pads again?

I know when you replace pads you should turn/replace the rotors, but what about the other way around?

 

No, you will be fine. I spent the summer swapping pads and rotors in all sorts of combinations due to the number of AX and Track events I attended. No issues.
Its not that black and white. You only turn/replace rotors if they need it, i.e. they have runout, cracks, too little metal left, etc.