In all of my experiences the copper drain tube and the rubber boot seal usually have to come off before removal or installation. They usually don't come apart from each other without the boot falling apart. I'm not even sure if the boot was soft and supple (like new) if the drain tube would come out very easily.

I've just always just used a flared piece of copper tubing with silicone sealant and that has worked pretty good. If you use an aftermarket rubber grommet, I have found that it sits too high and will create a lip that the condensate water can't get over to drain.