Hi @andrewsp11
We have members_post_error_message filter hook to change error message for Content Permissions feature, but it only takes $message parameter, so you cannot use excerpt there. I’m afraid that what you want to achieve requires custom development.
Best
Has this changed? I support a site that was developed about 3 years ago where the custom post excerpt was shown on an archive page to all users. I just noticed the error message and no excerpt after updating to the latest version today – but I haven’t visited this page recently.
[update] Never mind – one of the site editors made the posts private, thus the disappearing excerpts.