yeah, they plug right in. They may rotate the reverse direction though, so you will have to do the servo reverse mod on one of the servo's and then swap the two rear channels and possibly reverse some servo channels, but it should be as simple as that.

I am currently working on a write up for how to upgrade to the hs 55's

someone in another thread also mentioned that they have two different versions of the hs 55's, one that turns cc and cw, so if that is the case, then you wouldn't have to do the servo reverse mod.