Removing music from iPod?

Several ways. You could select "Manually Manage Music" and then drag and drop songs to your iPod (and then simply leave out what you don't want).

But assuming you want to keep autosync, you could tell the iPod to sync only checked songs. Once you have done this, in iTunes, make a playlist/smart playlist of your Christmas music. Select all the music you want to keep off the iPod, then right/ctrl click and select "uncheck selection" You will see the little box to the left of the track become unchecked.

Now you can keep the tracks in iTunes, but not sync them to the iPod. When Christmas rolls around and you want to sync, all you have to do is re-check the songs.