You can go back to the history state in the history panel of the develop module.
Also removing printer depends upon the OS, you can uninstall the printers that you do not need.
You can cancel operations in the upper left corner of the interface, under the Identity Plate. For example, if you're importing a set of images and want to cancel that operation, the progress bar under the Identity plate will have a small "X" at the end that you can click to cancel that operation.
Here's an example where I'm building 1:1 previews and can cancel by clicking the "X" where shown: