Most likely you can find plugins that do this, or you can write your own smart plugin.
Plugin development requires some skill and some time, but your task is not very complex. You could override it by enquing new stylesheets for the pages you define.
If you do make this, I'd also make an admin panel where you can specify which sheet for which page/post.
If your not that technical, you can simply look for a plugin.
Ps. the override stylesheet overrides the picture with !Important
For such small changes, I would not replace the main sheet.. though if you were to expand with a mobile edition with all definitions new, registerring and deregisterring sheets might be a good way to go.