Rather than “To view this content, you must be a member of XYZ’s Patreon at $N or more” I would like to input custom text for locked content, is this possible?
Thank you for this great plug-in 
Try going to Patreon Settings menu from WP admin and using the site-wide message input there. Some parts of that interface is hardcoded since it changes depending on the patron’s status and pledge though so you may not be able to change some of them.