I used the following filters:

Dim CustomerList = Me.company.Factories.CustomerFactory.List()
Dim filter = PropertyFilterExpression.Equal(PropertyFilterExpression.Property("Customer.ID"),
         PropertyFilterExpression.Constant(ID))
' Use LoadModifier to filter
Dim modifier = LoadModifiers.Create()
modifier.Filters = filter
' load customer based on filter expression And set as data source
CustomerList.Load(modifier)
selectedCustomer = CustomerList.First()

The ID is the id of the customer and the selectedCustomer will hold the customer with all of its properties.  This is in VB but the logic is the same for C#.  Me.company has to be filled by selecting the company and you also have to be authorised.

Savin after changing the properties can be bone by selectedCustomer.Save()