The Aethersprite (regardless of Pilot) states that they can spend 1 force point to perform a boost or barrel roll after fully performing a maneuver. My question is: can they do this even if they are stressed? Thanks.

No.

You cannot perform actions whilst stressed unless the source of the action speficially and explicitly says it can be used whilst stressed.

2 hours ago, Diamond_Spear said:

The Aethersprite (regardless of Pilot) states that they can spend 1 force point to perform a boost or barrel roll after fully performing a maneuver.

The Athersprites ability allows you to perform the boost or barrel roll action and therefore cannot be used while being stressed.

If it would just allow you to boost or barrel roll like you wrote, it could be used while being stressed, because it wouldn‘t be an action.

Card image for reference, Jedi Knight with Fine Tuned Controls ship ability:

Contrasting card as an example of something that does work after a red maneuver/while stressed, Afterburners:

Thanks everyone!