Well, I think you entered a bit of a legal grey area. You took an airplane that is not certified for flight into known icing conditions into what would be considered icing conditions but there was obviously no visible ice accumulation. The FAA has ALWAYS ruled in the past that there does NOT need to be a PIREP or Airmet for an area to be considered known icing conditions. It just needs to be below freezing with visible moisture.
Although there will be plenty of people on here who will disagree with me on the legality, it is how the FAA has ruled in the past whenever a pilot has been violated and used the defense, "well it wasn't reported." It doesn't have to be. My personal opinion is that what you did was not unsafe, you had an out, which is a must, even if you are going to have an airplane that is certified. Unless you are flying commercially (freight or passengers) you will probably not get much ice experience.