Adding a new column in Privatemsg 7.x

Hi,

I'd like to modify privatemsg to suit my needs with custom columns. I want to add 1 or 2 more columns in the header along with data.

As I read the instructions in privatemsg.theme.inc:

* Three requirements have to be fulfilled so a new column, with data, is
* displayed in the private message list:
* - A field needs to be returned by the list query, see @link sql Query Builder @endlink.
* - A header theme pattern needs to exist for the field.
* - A field theme pattern needs to exist for the field.

Does that mean I have to implement these 3 hooks?
- hook_query_privatemsg_sql_list_alter
- theme_privatemsg_list_header
- theme_privatemsg_list_field

If so, can anyone please give more specific instructs on how to do the above? Sample code would be best. Thank you in advance.