is there a way to edit/change picture in picture setup in imovie

As I understand you, you are using PiP to make a collage of faces and need more space so you can add more faces.

If you are making a collage then you must be sharing out and importing back in after adding each face. Correct?

Assuming that the above is your procedure I see no way to reorganize the space without starting over.

— Rich

Yes, it's hard to add new faces to the collage without doing it over if there's not enough space.

Maybe you can add the new faces to a new collage and do a split screen with the old one.

-- Rich

No, you cannot change the basic picture in picture setup in iMovie. It is built into the app.

To make sure that we are on the same page, what kind of edit/change did you have in mind?

-- Rich