Your post is somewhat confusing. Are you stating that you have two addresses, but currently your primary residence is in the state of Washington and you also have a Washington carry permit?
You can OC in Michigan, and if your carry permit from Washington allows you to CC, then you can CC here, too. It doesn't matter if you have a second place in MI, if your primary residence is in WA then you can conceal carry under their license. Once your primary residence changes to MI then you must get a MI CPL to CC here because MI doesn't recognize out-of-state licenses for MI residents, although you can still OC without one. Note that there are extra restrictions on OCing without a license that allows you to CC from any state.
As long as your primary residence is not MI your pistols do not have to be registered.