That message might appear even if you don't physically change component but, depending on the mainboard, a bios update or a ide drivers update or overclocking might trigger it. Changing very low level drivers (like going from Ide to Ahci drivers) might also cause the system to get a new hardware ID.
However, fact you had to reactivate, doesn't necessarily mean you *consumed* one of your activations, because the activation system recognizes between minor or major system changes.
The only time you should worry, is if you get the message about having used all your activations, that would be the ONLY time you ever need to contact us.
Don't forget that, if the last activation was granted less than 90 days earlier, the oldest activations will be reclaimed to make space for new ones, even if you used all your 6 and without having to contact us.
Is really difficult, with all these safety measures in, to end up without activations left.