Thank you to everyone who searched high and low for those codes! You have my appreciation.
Be our Guinea Pig and find out! j/k: As long as you don't type "iroll20s" you'll be fine. (And even if you're not, disabling achievements doesn't carry over from one save game to the next.) I can confirm that Steam achievements are NOT disabled by using the pet codes. I have all 3 pets and have just unlocked my first achievement.