Mechanically speaking, it's a single weapon split in two, not two different weapons combining into one, so I'd say "No, unless they're identical weapons" (like swapping bayonets between muskets).
Sadly, no... I've yet to come up with a way for multiple weapons to combine and turn into something different without making it too powerful or too weak...
Fortunatelly, between Alternate Damage Type, Double and Extendable, there are a lot of ways to create "transforming" weapons (who is to say that Alternate Damage Modification isn't your spear turning into a pole-hammer, rather than just a pole weapon with both a spike and a hammer at its end?)