Inadvertent Whistle?

[just another ref]

No internet for five days, other than my phone. This thread comes at this question from a slightly different angle than others. The calling official gives a signal which he immediately realizes is a mistake and would like to change. Picture this: I anticipate a block, then the defender gets in position quicker than I thought possible, resulting in a clear charge. I see the play, but my hands don't get the memo in time. I mistakenly signal the block preliminary, then immediately realize the error. I go to the table and report the charge. All this is okay, unless there was a double whistle and my partner gave the charge signal all the way, in which case we must report a double foul?

I would like to know the intent and purpose of this rule.