I would stronly adwise not to do that. You may take a look at allow updates Option in BOL.

>Hi everyones,
>
>I want to add a column in master.sysusers In query analyser, I used this syntax:
>
>alter table sysusers add suid as smallint
>
>and I got this error:
>
>Server: Msg 1706, Level 16, State 4, Line 1
>System table 'sysusers' was not created, because ad hoc updates to system catalogs are not enabled.
>
>What can I do?
>
>It's a one shot deal, I want to do it only once. I need this because I run an old application design for SQL7 on a SQL2000 and in SQL7, the column suid existed. I don't care about the value itself, I can fill it in manually once it's created.
>
>TIA,
>Diane Robitaille eng.