I have a suggestion mate. Something wfas should have had in the first place IMO. And all the items you need are already in the game, so I take it doing it wouldn't be much of a challange.
Along with musketeers and pikemen, 17th century armored cuirassiers were one of the most iconic troops of the period.
Equipped with a sexy plate armor, armet, and a pistol, such cuirassiers were popular troughout Europe, but started declining and being replaced by lighter cavalry around 1650's, although they were undoubtedly still used.
While black armor was the most common among cuirassiers, differently colored armors existed, especially in the thirty years war. Many of them decorated their helmets with plumes(again, especially in the thirty years war) and shashes, as seen in on the modeled black cuirassier.
To sum it up. You've got exactly such armor in wfas. Only Swedish generals use it though(as far as I know) and armets two handed swordsmen use are downright perfect for cuirassiers. All you have to do is color them black, which is an easy enough job I think, especially for you. Equip them with an above-average - good pistol and a sword(basically the equipment of Swedish reiters) and you're good to go. Make them a Swedish unit but also recruitable in a Swedish mercenary camp. Make them one of the most expensive troops. Expensive to buy, expensiver to maintain. (If nothing, as costly as a Swedish Reiter)
Now don't remove Swedish Reiters though. Although Swedish Reiters are rather fictional. They are pretty badass too.
Here's a few more armors to gorge your eyes, as well as show you another helmet used by cuirassiers, if you want a little more variation within unit looks.