I DM an AL group of four. They agree to create new level 1 characters (they are experienced), but ask me to adjust the combat to give maximum possible XP in an adventure, in case they miss out the non-combat XP reward, so they can advance more quickly.
The easiest to do this is by increasing the number of enemies, especially the less threatening ones, like kobolds, zombies, etc.
I try to search AL DMG and found this part (emphasis mine):
You can also adjust the adventure on the fly, beyond the guidelines given in the adventure, or make other changes as you see fit in order to insure your players have a good time.
AL FAQ (emphasis mine):
Sometimes characters fall behind the adventure’s expected level. In these situations, there are two main methods of supplementing character experience. [...]
Random Encounters. You can’t grant players roleplaying experience to make up the deficit; however, they may add random encounters as needed (assuming the adventure provides a list of random encounters). See below for more guidance on random encounters.
The FAQ states that to give more XP to players, you can only use two methods, one of them is giving random encounter, if the adventure has a list of random of encounter.
This makes me think that adding more enemies (or changing the enemies with more XP ones) for the sole reason of guaranteeing maximum XP for each adventure is not in line with the spirit of AL, and wondering if this is ever within the bounds of AL DM "empowered to alter an encounter".
Is giving more enemies than the guidelines (for very strong) or changing the types, for the reason to guarantee max XP, allowed for an AL DM?