I believe that common sense should be your guide.
One year I picked up my permit in Atikokan and they had a fire ban on even though it had been raining fairly heavy and the forecast was for more rain the next few days.

I asked the lady whether or not the ban would be lifted in the next few days?
She said that it wasn't their call but that obviously the fire danger was greatly diminished and I should use my best judgment.

I said that with the cooler temps forecast for start of trip that a nice warm campfire was something I looked would welcome after a long day on the water.

She smiled and said they wouldn't want anyone suffering hypothermia or being miserable when the conditions had obviously changed but the ban hadn't been officially lifted yet.

When I hit Beaverhouse, it was raining buckets and at the portage to Quetico lk, I ran into a Father and Daughter tandem who said the last few days had been miserable with the cold/wind and rain, but they were afraid to build a fire becasue when they went in a fire ban was on.

I told them it still was and what the ranger gal told me and that I planned a fire that night, ban or no ban.
The Father looked a little sheepish and the daughter said something like " I told you they wouldn't care, it's been raining cats/dogs for the last 3 days.

I can't imagine a back country ranger going without a fire when the conditions changed before the ban could be officially lifted, and doubt very much they would expect you to do the same.