Billing during extension of Service Contract

Hi,

Needed help on understanding Billing schedules on Service Contract when extended.Assume that I have a contract which has a service line with price entered manually as as $1200 for 12 months The billing schedule is set at $100 per month for the contract period of 1 year. When I extend the contract to say 6 months, how do I ensure that contract extension automatically extends the service line to six months and billing schedule shows 6 more lines of $100 each.

We have a scenario to programmatically create and update a Service Agreement from OM order. We wanted to ensure that standard extension will update service line to extended period and $1200 is extended to $1800, This should add 6 more biiling lines in Billing Schedule.