Credit Memo Adjustment

[jennialea]

I updated a Credit Memo in Sales Order with an incorrect invoice date.
I tried to adjust the CM by:
AR
Main
Invoice Data Entry
This will not let me print or update.

Is there any other way to adjust?
Would creating a debit memo to cancel out the CM work?
and if so would i delete commission amounts so it does not affect the salesperson commission report?

Any help would be greatly appreciated
Thanks!