Title speaks for itself.
Can you for example have a model wit a shield, 1H weapon, and a pistol (which doesn't break the 2-weapon limit); fire the pistol on one turn, then switch to the melee weapon on the next turn for making a charge?
Alternatively, can you have a model with an arcane wand and a flintlock rifle who uses the rifle to shoot on one turn, then switches to the wand the next turn to aid in casting a spell?
Weapon swaps are perfectly legal. You can use any equipment you have on a model so long as there's nothing explicitly preventing you from doing so, i.e. attempting to use a two-handed sword while holding a shield.
And, obviously, attacking costs an Action, so you can't shoot something across the table and then turn around to bop someone on the head in the same turn.