I have a defined a TikZ style "midcircle" that decorates a path with, say, a small circle in the middle (with the decorations.markings library, setting "pos=0.5"). E.g.
would draw a straight line with a circle in the middle. Now I would like to be able to change the position of the circle by defining another style, say "midcirclepos", such that e.g.
would draw the circle at "pos=0.7" instead "pos=0.5". I think I've seen such constructions, but I can't find any more how to implement it.
By the way, I can't use the usual default arguments for TikZ styles, because my "midcircle" already takes other arguments that also have defaults.