If you enter a value in each player's custom value column, you can make it total to get a team custom value.
Enter your ratings/MPRs/whatever in a custom value column under players. (Menu > Manage > Players/Teams > Players)
Then go to Teams (Menu > Manage > Players/Teams > Teams)
Click on Display More Options (top right)
Click on Update Custom Values or Update Div Custom Values, which ever one you entered the information in.
****If you only want to update a specific division, select the division first. This will only update that division's custom values.
If you want to get a team total for all teams that have player custom values, choose the ALL under divisions.