Certainly doable. You'll want to mount the tower to the countertop. The existing tower should be able to be mounted to the counter using apropriate screws, unless it's granite/ceramic/tile/etc, then you would want to use bolts and nuts.
You'll probably want to drill a new hole in the top of the unit using a 2 1/2" hole saw. Cooling lines won't run through the top, but I would take off the top of the unit to verify you're not hitting any vital components. Seal up the old hole with some insulation. Then you want a piece of PVC to bridge any gap between the unit and the counter, and I would seal that connection as well.
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Sometimes when I reflect back on all the beer I drink I feel ashamed.
Then I look into the glass and think about the workers in the brewery
and all of their hopes and dreams. If I didn't drink this beer, they might
be out of work and their dreams would be shattered. Then I say to myself,
"It is better that I drink this beer and let their dreams come true than
be selfish and worry about my liver."
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