I'd like to file the baffle down on a
metal otto link for tenor.
I heard this would make the mouthpiece play
 darker. how would I go about doing this
without ruining it.

Thanks

Use a needle file and stay away from the tip rail.  Being, a Link, you may
already have a straight baffle.  But if it is a roll-over or short straight
baffle, you can try to remove it.

http://www.mouthpieceheaven.com/content/baffle.htm#straight

After you get it the way you like it, wrap various grades of sandpaper
around your file to get a smoother finish.  

You may want to place a piece of electrical tape on your tip rail and side
rails to protect them from your slips.  

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