Ridge Runner,
I believe it is the other way around. If you buy an Encore as a rifle, you can not change it to a pistol unless you pay a $200 processing fee each time you want change it. (Of course you must follow the 15” or less for pistols (handgrip) and 16” or greater for rifles (buttstock) barrel regulations.) However, if you buy the Encore as a pistol it is registered as a pistol (thus the additional background check and longer waiting period in Wisconsin) and you can change it back and forth as often as you want with out notification to anyone (again following the pistol and rifle barrel length regulations you stated). I called the Bureau of Alcohol, Tobacco, and Firearms (ATF) offices in Wisconsin and didn’t get a clear response. But the forums I read before purchasing my T/C Encore pistol gave that reasoning. Certain stores only sell the encore as a black powder gun, because they do not sell handguns. This means you wouldn’t be able to legally change that Encore to a pistol (pistol grip and 15” or less barrel) with out registering it has a hand gun first. So my understanding is that if you are going to buy an Encore and want to use it legally as a pistol, purchase it as a pistol with the additional paperwork and then buy the buttstock and barrel of your rifle, shotgun, black powder (with appropriate fore end) accessories as you need them.