I don't know about the legal aspects of flashing all the trailer lights either. I have seen some semi truckers flashing their clearance lights while getting up to highway speed but always thought they were doing it manually.
I wouldn't think the police would say anything as long as it was a short term situation that made sense.
I almost got rear ended the other day after merging onto I-75. I was almost up to 60 in the far right lane when I heard tires squealing somewhere. Finally saw a car in my mirror sliding almost sideways right behind me. Must have thought I was going 75 like everyone else. Fortunately he got it under control without hitting me.