From what you post,I understand that you had opted for CP when you filed your 140, right?
Then you filed for AOS.
Now you again want to go for CP.
Am I right?
Well, in my personal opinion, you could do that,however, it would involve expenses, waste of time and more importantly,this whole thing might leave the CIS confused (as it is, they frequently get confused even in straight forward cases).
So,if you have job-guarantee,then perhaps leave it for AOS.
Hopefully, some other experienced gurus here may be able to give their opinion or better still, consult an attorney.