YB,

IMHO Nope. Just configure the set up differently next year. It just something you do not want to do over the long term. YouTube has many videos explaining the process for DIYers. Aloha

I asked the same question in the professional forum earlier in the fall. You can see they didn't really agree, but it seems like the "right" way to do it is drain the backflow separately and then blow out the system after the backflow with the valve closed between where you have the air connected and the backflow.

It won't cause any problem with trapped air, the problem with blowing out through the backflow seems to be that if you are using a powerful enough compressor (which most homeowners don't use) you could end up overheating some of the parts in the backflow and maybe getting oil from the compressor into your household pipes.

After reading everything I cut into my mainline after the backflow and put in a valve for winterizing, just to be safe.

Here is a link that might be useful: Winterizing Thread