Another route to enable low-gravity with a trigger, is by changing the player's gravity through an AddOutput.
You can use a trigger in your map that you already have such as a trigger_multiple, trigger_push, trigger_teleport, etc or even a button and put an output on it to give them gravity. The output would look something like this:
Output|Target|Input|Parameter
OnSomething|!activator|AddOutput|gravity [? - ?]
for a button it'd be OnPressed or OnDamaged and for a trigger it'd be OnStartTouch. the value of gravity is a percentage of the base value so .5 is half the gravity and 2 is double it.