What are the Shar’i limits of the eyebrow beyond which it is permissible to trim excess hair, and is it permissible to trim hair that has grown longer due to excessive eyebrow plucking?

There is no harm in removing hair that grows outside the eyebrow bone, because it is considered facial hair. If eyebrow hair increases beyond the usual extent, causing harm or disfiguring one's appearance, it is permissible to remove it until it returns to the normal eyebrow shape.