Hi seanpears99,

No, sorry. No combination of task type is going to allow you to chance dates manually and increase duration. When you manually enter a finish date, Project sets a FNET (finish no earlier than) constraint, maintains the duration, and moves the start date.

The only work around would be to set the task at a low level (1%) complete which sets an Actual Start date. If you then change finish date, the start date will not move.