Cannot add User field to printers.conf

I need to specify a different user name when printing in my enterprise environment; e.g. by setting User xxxx in my cups configuration.

I have tried doing sudo su; service cups stop; then editing my printers.conf file to add User xxxx in the options for the printer, and then service cups start. However, within a minute or so, the printers.conf gets overwritten and the User line is removed.

How can I keep this change?