OK so far I haven't broken anything, I actually forgot my thermal paste so I can't install it today..
I assembled the cooler (fan & pins) and was trying to figure out how it goes.
I can already see myself having a tough time aligning all the pins (it's my first time with push-pins).
OK so they should be turned clock-wise so that they don't pop out again. So far so good.
However, I've been trying to pop some of the pins, outside the motherboard of course, and I can't do it 
outside the motherboard!!
And I can see no way how I'd be able to get my finger underneath the cooler above the motherboard to push them either (assuming I can manage to push them)..
I found advice saying that it's better to install the cooler with the motherboard outside of the case.
But outside the case, I'd have no way to hold the motherboard steady.. while in the case it's steady and I can see the back of the motherboard very clearly.
Any tips or tricks please?