Hi,
The simplest method for this would be to set the IsServerAdminSite=1 for the 2nd site in the mp_Sites table in your database. You should then set IsServerAdminSite=0 for the first site.
Your SiteIDs will remain the same but you will achieve the effect of having the 2nd site as your Admin site.
I definitely suggest you make a backup of your database before attempting this change.
HTH,
Joe D.