I tried putting the clips in the slots in the skirt, but the slots are so big and roomy that the clips just kept falling out. How did you keep them in place and as close to the studs as possible before pushing in the skirt?
What I ended up doing was leaving the clips on the studs on the car, lining up the skirt in its final position, then gently pushing the skirt onto the top groove of the clips one at a time from left to right. I found that that method worked like a charm without breaking anything. YMMV.
In any case, I agree that "sliding" the skirt back onto the underbody is unworkable; I don't see how it's physically possible, given the position of the "hook" at the end of the skirt relative to the slot it must fit into (i.e., moving the skirt to the right so that you can slide it onto the clips going left moves the hook out of position). Sounds confusing, but anyone trying the skirt refitting process by sliding it back on should know what I'm talking about.