'Access denied' page customization

When I set page permissions for members with specific role, other members get a page saying: ‘You don’t have permissions to access this page’ + ‘Back to site’ OR ‘Switch account’ (see attached image).
I’d be nice if I could customize this page. I’d like to inform these members how to apply for permission.
(Or maybe it is possible somehow, and I just don’t know how?)

Thanks,

Agreed! I just created a member’s area and I would like to be able to have a slightly gentler message.

how to customize this page,