Hi
Might need to experiment first. The effects like rotation are designed to work on the whole clip. More importantly is that cropping will remove a significant part of the image area depending on the degree of rotation needed to re-orientate the full frame. Assuming you would require to maintain a full frame then Zoom instead of crop would be required.
e.g. Original slanted image...

Now the image has been rotated back to horizontal....

The rotation has introduced transparent corners. (Which will appear black in the sequence preview). The size of these depends on the original rotation. This example was around 15 degrees of tilt
Crop will cut these corners off of course but will reduce the size of the frame......and probably won't be centralized as in this example.

Instead of using the Crop effect you require to use the Zoom effect.... This will keep the final result full frame....
Constrain the AR to 16:9 to achieve this.

As you can see, quite a lot of the frame is lost even with a 15 degree tilt. This example uses a single image (frame) with VP. Setting up this using keyframes, even for significant points in a clip may not be very successful. But you can try! 🙂
Nat