The approach that Alfresco has taken, and with which I have come to agree, is that the created and modified information is a function of the Alfresco repository and does not "belong" to the document owner. They represent information that is known to Alfresco, and for which Alfresco is the source.
To deal with what your customer (and many other people want), you should, according to Alfresco, create a customized aspect that replicates those properties. The information in those properties belongs to the document owner (your customer) and he is free to change them as needed. You may need to provide some custom changes so that those values are displayed rather than those for cm:auditable, but you have the source code.