Custom "Authorization Required" Message on Login Page?

Is there a simple way to edit the message that displays on the login page when using this plugin?
Right now it says "Authorization Required: This blog may only be viewed by users who are subscribed to this blog" and I just want to change the text of that message.

I found this thread (https://premium.wpmudev.org/forums/topic/on-multisite-privacy-is-there-away-to-change-the-access-denied-page-to-have-a-custom-landing-page) detailing a fix with a child theme, but I'm looking for something simpler.

P.S. I am also planning to use the plugins Login Message and Ultimate Branding to customize the login screen, if that makes a difference. Thanks!