Permission to edit Partner Contribution % on Sales Orders

Users may give permission to custom roles to edit the Partner's Contribution % on Sales Order.

To have this, follow the steps below:
1. Using an Administrator role, navigate to Setup > Users/Roles > Manage Roles.
2. Click Edit on the custom role that needs the permission.
3. Under the Permission tab > Setup subtab > Add Partner Contribution | Access Level = Full
4. Click Save.