Consuming AIF Document Sales Order Service - Update Sales Order w/ multiple sales lines

Service consumed in c# application.  Would like to find a way using c# to dynamically assign updated values to one or many sales lines.  Is something like the psuedo code below possible to do with the sales line object, or would I need to use a some type of template with place holders assigned to all the field that could be updated?  I would appreciate it if someone could point me in the best direction to accomplish.

My c# app can pass  1) a unique sales line value ( IvTransID ),  2) name of field to update < fieldName > and  3) the new value < newValue >

. . .

AxdSalesOrder _SalesOrder = _Client.read(_callContext, entityKeys);
AxdEntity_SalesTable _SalesOrderTable = _SalesOrder.SalesTable[0];

for (int j = 0; j < _SalesOrder.SalesTable[0].SalesLine.Count(); j++)
{
      if (_SalesOrder.SalesTable[0].SalesLine[j].InventTransId == ivTransID )
                 SalesOrder.SalesTable[0].SalesLine[j].< field > = < newValue > ;

      . . .