move the iMovie Theater to external drive

Hello,

On my MacBook, I have moved the iMovie Library and iMovie Theatre files to an external drive but every time I open iMovie it reinstalls the iMovie Theatre file to the original location.

My MacBook has very limited internal storage. Is this just the way iMovie is?

Do I just have to drag the file to the external and delete it on the internal every time I use iMovie?

Cheers