Bruce Gordon BLT, Cannondale parts bike, Ecodyne recumbent trike, Counterpoint Opus 2, miyata 1000
1. No, racks do not have to be bolted on, if you ride very smooth roads and are not going to use them for very long. Not sure how you would do it but anything is possible.
2. See last sentence above. You want to snap a couple of quick releases to change your bike from a commuter to a racer? The common way to do that is to get two bikes. Sorry, it must be terrible to have to get another bike .