I don't believe cooling will cause a respiratory infection. Myself and many others cool our Bci to a NTL of 72 to 75 and our Bcc 68 to 72. As long as you give them a day temp of about 80-82 they will be fine. A healthy boa with no other illness or virus will not get respiratory infections during a cool period.
If your boas get a respiratory infection during cool down this means 1. it is being kept to cold at night (below 68) or 2. it is not receiving adequate day time temps or 3. its immune system is already weakened from some other illness.
None of my 20 boas have ever gotten sick during this cycling.

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