[Alexandre Braso]

You will export separate file with alpha?
if you thing export RGB+Alpha you have no options, need to be unconpressed.

Alexandre Braso
http://www.pixelsrender.com.br

[Alexandre Braso]

The collect files will do exactly that you want, copy your files and don´t touch your original files.
be atention to your project folders organization, the copy of your project will follow de organization of the project and not the organization of your original files.

Alexandre Braso
http://www.pixelsrender.com.br

[Alexandre Braso]

you can replace one footage(or precomp) just selecting it in the timeline panel and then selecting other footage(or precomp) in project panel and draging over original in timeline panel while press opt(ctrl on pc).
i thing it can help you.

Alexandre Braso
http://www.pixelsrender.com.br

[Alexandre Braso]

You can do that selecting these keyframes and release Alt(pc) or Opt(mac) while click and move the first ou last keyframe.

Alexandre Braso
http://www.pixelsrender.com.br

[Alexandre Braso]

Well…
i don’t know if i really undertand your problem, but i think you can sold it making a copy of your background layer, put the 2 layers of the background side by side, create a null object to manipulate de layers, make a keyframe in position of null to start position with the first layer at the center of the composition and a end position with the second layer at the center the composition, create a loop out expression in the position property of null object and enable motion blur if you want.

Alexandre Braso
http://www.pixelsrender.com.br