P1. Any actor would be eager to play a lead role at a festival this prestigious.
This principle suggests that the prestige of the festival might attract talented actors, but it doesn't specifically argue for casting a professional actor over a troupe member. Not useful.
P2. An organization should not alter regular practices unless they have failed to produce results.
This principle supports the idea of maintaining the current successful practice of casting from within the troupe unless it is proven ineffective, arguing against bringing in an outsider. Hence, supports the option of Casting from the troupe.
P3. A theatre troupe should cast actors with the most experience in stage acting in lead roles.
This principle supports casting the most experienced actor available, likely advocating for a professional actor if they have more experience than the troupe members. However, doesn't weighs towards either professional actor (Ringer) or an actor from existing troupe. Hence, not useful.
P4. In casting any role, a theatre troupe must take care not to alienate its members.
This principle suggests the importance of maintaining troupe morale and cohesion, advocating for casting from within the troupe to avoid upsetting the regular members. While this principle supports casting from the troupe option, however P2 seems to be more direct.
P5. Theatre troupes often deliver exceptional performances when they cast professional actors.
This principle argues that bringing in a professional actor can lead to better performances, supporting the idea of casting a ringer for the lead role. Supports casting a Ringer.
Answer
P5 - Casting a Ringer
P2 - Casting from the troupe