Re: Constitution, Miranda, and Constelation Class
The Oberth is a good example of this - it's easy to swap out the lower pod and stick something in its place, as Jackill did with his light tug variant.
Unfortunately, there's never been any instance in canon Trek where that was even remotely the case with an Oberth.
(Sorry, you'll have to forgive my whine...I just hate that ship so much
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