This is my answer not only to this question, but to any and all questions about whether it's okay or a good idea to go back and change stuff.

The whole reason for October Prep is that it is an eminently better idea to do so in the middle of October than in the middle of November. In fact, I will go as far as to say, we're doing this because doing it in November is an awful idea.

So by all means, change it. Rip it up and start over, even (although you might want to go through as much of the previous exercises as you can, to make sure the new idea works.)

...
Regards,
Eric Fretheim
Assistant Prep Leader, 2015 October NaNoWriMo Prep Challenge

"It is perfectly okay to write garbage-- as long as you edit brilliantly." ~C.J. Cherryh

“No, writing 50,000 words in a month is normal. You are not crazy. This is not insane.” ~Teri Brown