I like to change foot/toe position with both leg press and extension. I find I can hit the different muscle of the quads doing so. One technique (I guess its a technique, maybe its a method...anyways) I use on leg press is to change foot position with each set, ends up almost like a rest-pause set of sorts, but it doesn't end. First, I'll have a wide stance, feet parallel, next set wide stance toes pointed out, next set narrow stance feet parallel, next set toes in and touching. Each set can target a different muscle primarily. I find that the toes touching nails the tear drop really good. Also, I place my feet on the platform such that my knees don't go past my toes on the negative portion of the movement.
I do something similar on the extensions as well. I feel I can consciously engage a certain muscle more depending on the direction my toes are pointing. Unlike the leg press, I can engage the VL better when my toes are pointed in, and the tear drop when pointed out for example. Often, I use lighter weight and higher reps when doing leg extensions to take the tension off the knee, plus I get a fantastic pump.