I thought the trigger for the first action would be the button over each menu item, then the conditional action would trigger on slide exit. The issue I saw with having it all in one action is that I couldn't work out how to pause the next part of the action (jump to the slide associated with the menu item) and let the zoom effect finish. So the first action is only for the zoom on a button click, the second action jumps at the exit of the slide, after the zoom has finished. I'm interested to see how it would be done in one action (and save having to create another action on the slide).
In the past when I have needed to simulate an effect similar to what you describe what I did was to have the animation effect set up on a separate slide entirely. So I had one slide as the menu slide and clicking items on that slide would jump the user to an intermediate slide that shows the effect (this slide was usually only a second or so in duration) and then as soon as that slide ended, it continued to the slide that started the relevant content section.
So the trick here is that although the content starts on the slide AFTER the animation slide, you point the menu object to jump to the animation slide, not the content slide.