I have two sets of wheels, one with slick tires I use for commuting and one with knobbies for off road, if I want to run different cassettes on each wheel will I have to adjust my derailleur every time I swap them? I want to go from a 11-28 to 11-32
If the cassettes are in the same position then not. If they are slightly offset sideways from each other then you may have to adjust the cable to make them change perfectly.
The other factor is, because the 32 sprocket is slightly larger diameter, you need to check if the top jockey wheel is set correctly. You do this by adjusting the "B" screw to get the jockey as near to the cassette as possible without it catching. This gives the best position for gear changing.
I swap wheels about with generally no bother. Just make sure first that the derailleur isn't going to catch the spokes. !!
Ride hard or ride home alone!
I have tried putting a random cassette on a bike, hoping to make a cheap repair, but it only caused me more problems, my friend started complaining about not bein able to use all the gears despite 5 or 6 adjustments to the derailer. Sometimes it works some times it doesn't, Your chain needs to be compatible with that number of speeds as well.