Ya, I agree. Actually, the Galaxy-X is really not "Offical". Remember, its very possible the Galaxy-X is only built in that other time line in the final episode in TNG. But assuming for a moment that Starfleet does make an extensive refit like this in the future, I would imagine that the Original Galaxy looses its Saucer Section Seperation Capability. As seen on the ship, the Heavy Phaser Cannon looks litterly connected too the secondary hull and the Embelicals connections between both ships might be so extensive that it would be impractical too have seperation anymore. Also, I would like too add that its possible not all Galaxies received this refit. Its possible only some of the Galaxies received this refit too make a "Pocket Dreadnaughnt/Battleship" and it might be fairly expensive and time consuming too refit a Galay like this. SFB had many ships built like this but they usually where not a mainstream class of vessel. Usually used as Fleet Leaders or Variants too componsate for a Class a race didn't have.