I'm assuming you want one servo channel to have 4 output settings, if so here is another option, create a new mixer, call it lights if you like, with two input lines, first with a curve which you can set each end point (or use the curves menu) controlled with a 3 way switch which you can program in 3 settings in mixer curve, you may need to adjust the centre position in the servo calibrate menu to get one position, then on the 2nd line create a mixer with a fixed value input, then assign a two way switch to switch between the two lines.
