Uh I can think of at least two other classes that were explicitly designed for that, one of which was actually converted in full. The Mogami class cruisers were built with 5 triple 155mm guns but were converted to twin 203mm guns as designed after Japan left the Naval Treaty system. And the Yamato class were designed with triple 46cm guns but were meant to eventually swap out to twin 51cm guns, though I can't find the source for that I've read that in multiple placesSwapping out a battleship turret is a bit more involved, especially considering that the turret is only part of the weapon system, there is also the ammunition handling and storage areas below deck that would have to be refitted. There was only ever one ship class designed with this in mind (Scharnhorst) and the swap was never carried out. Building a turret for 16"/50 and only fitting 16"/45s is a bit more practical as the actual gun sub assemblies are designed to be replaced occasionally due to wear and tear from firing. Would probably still take a while, not something you particularly want to be doing to your heavy fleet units in the midst of a conflict. Taking them out of action for a month or two and thus depleting your fleet strength vs having a marginally less effective gun. seems like a poor choice to make.
Admittedly this proves the point, the Mogami's took a two year reconstruction to go from triple 155mm to twin 203mm's, though part of that was fixing the Top Heaviness of the class and QC issues with the welding