caldera_forms_render_notices-customize-error-notice.php

<?php
//Change error message of AJAX submitted form.
add_filter( 'caldera_forms_render_notices', function( $notices ){
	//Will NOT be set (during AJAX return) if there is no error
	if( isset( $notices[ 'error' ], $notices[ 'error' ][ 'note' ] ) ){
		$notices[ 'error' ][ 'note' ] = 'Form could not be submitted, please correct erorrs or give us a call.';
	}

	return $notices;
});

caldera_forms_render_notices-success.php

<?php
//Change success message of AJAX submitted form.
add_filter( 'caldera_forms_render_notices', function( $notices ){
	if( isset( $notices[ 'success' ], $notices[ 'success' ][ 'note' ] ) ){
		$notices[ 'success' ][ 'note' ] = 'That was awesome!';
	}
	return $notices;
});

Corrected success message code originally posted here: https://calderaforms.com/doc/caldera_forms_render_notices/