How to lock only position and size of image frames?

I have a large number of images layed out across many pages.

Each image frame has a very specific size and position.

While the frames will always maintain the same position and size, the image content within the frames are continually being changed.

I'm lookin for a way to lock only the size and position of the frames, so that they don't inadvertently get nudged out of place, or somehow accidentally get their size changed. Even a slight change of a fraction of an inch would be bad. However, even with position and size locked, I still would need to be able to select the frames and change their content, either by using "paste into..." to paste an image copied to the clipboard, or by using "place..." to insert a new image.

Is there a way to do that?

I feel like there should be, but couldn't find it.