Guild Wars 2

Is there a mechanic in place to prevent someone from guild hopping and racking up 100+ commendations and multiple pre-cursors on the first day?

well besides the fact that there is a 1 week research time so no one will be doing any missions the first day, it is also limited to 1 reward for each mission type per week. Regardless of how many guilds you are in.

TheDaiBish.9735:

“Remember that you can receive that reward once per Mission-type per week, but that’s still nothing to sniff at.”

http://massively.joystiq.com/2013/02/26/flameseeker-chronicles-the-gathering-storm-preview/

So no, you can only get them once a week.