Closing a Form Without Removing its Elements

Simplest way is to make a 'new' under the 'Forms' section of your table settings and set it up so that form only has the message you want to communicate. You can then set that form as the default for this submitter role for the time being. Or only set it for the 'Add Form' setting so that people hit this new form only when they're adding new entries. 

This way you leave your current form untouched and can just re-assign it if or when you need to re-open it.