Change Default Group in Script

Is it possible to change a user's default group inside a script for the duration of that script's execution?

I need to generate files in a script that have the proper user and group but my user's primary group is not who should own the resultant output.

$ groups
groupa groupb

$ ./myscript.sh

$ ls -l
-rw-r--r-- 1 me groupa     0 Sep 17 09:42 myscript_output.txt

But I want "groupb".

myscript.sh:

#!/bin/bash

touch "myscript_output.txt"