No. Magento does a lot of calculations when you create a creditmemo.

the sales table is changed and the *_canceled columns are filled. Same for order_item and *_refunded column.

IF you really want to do this and I highly disadvise to do so, you could do a dump of the database locally, create a creditmemo and then diff the dump before and after to get a feeling for what changes.

Please read the comment by @Simon!
> I do not think that creating a creditmemo fills any *_canceled column. These are filled when you actually cancel an order. 

Not sure about this, so I leave it up to you to check - if you checked on that, PLEASE EDIT THIS POST! :D