Yes, depending on your current version of minecraft, you can update it to completely start on a new slate (deletes all modifications). Or, you can open the minecraft.jar file using Winrar and manually undo what you replace. Or even un-install minecraft and re-install it using your previous licence.
Not in the current Vanilla (Minecraft without Mods) Minecraft, no. But their are a few Mods out there that will make that possible.
Not without mods.
Without mods, you can't.
you can get mods off websites like minecaft mods that no one uploads viruses to because they would get caught and banned in seconds, i reccomed minecraft mods.
There is no brass in MineCraft without mods.
TNT without mods. With mods, the hydrogen bomb.
When you download an update for Minecraft it deletes the entire .minecraft directory and re-downloads it. This will wipe any mods or texture packs installed.
Yup.
you cant without mods
you can get minecraft mods and textures off the minecraft mods website.
You don't need a CD for mods. You don't need a CD for Minecraft at all.
You cannot make a hang glider in Minecraft without mods.