Does anyone remember Gus Rentfro? Some folks here, I'm included, have boas from his Rio Bravo lines.
Gus used to post frequently on various boards and he was/is an authority on the boa constrictor. I was able to chat with him by e-mail a few times years ago.
One quote I remember went something like this. "It is nearly impossible to under feed a boa constrictor but it is entirely possibly to over feed one".
That may not be the exact wording he used but the message is what is important.
I look at the shed process as an excellent time to let a snake clean out and reenergize. The shed process utilizes energy as does digestion, I don't like to mix the two. I prefer to let the shed take place, which is almost always followed by some type of waste elimination and a period of inactivity then feed afterwards.
If you are feeding a boa constrictor prior to it eliminating waste from the previous feed, you are likely over feeding.
CAN you feed a boa during shed? Sure you can.
There is really no need to do so though.
If you are going to concentrate on anything during the shed process, make it about maintaining proper humidity levels in the enclosure and providing security for the animal.