transitioning from thawed mouse to crickets or ZM pacman frog food

According to the place where I got my pacman from, he was being fed 2 thawed mice once a week.

How hard is it to transition an adult pacman from mice to crickets or even ZM pacman frog food?

Pacman Frog Food

Impossible to predict that process. Your Pacman could eat insects or night crawlers on the first time offered; or refuse to eat anything different than mice for a long time.

As Carlos said, it can be hard to guess how your frog will react. Most pacmans aren't picky on what food you put in front of them.
Your doing the right thing for your frog trying to get him on a healthier diet!