exclude-category.php

<?php
/**
 * Limit Caldera Forms post type select to EXCLUDE a category.
 */
add_filter( 'caldera_forms_autopopulate_post_type_args', function( $args, $field ) {

	//IMPORTANT change this to match your field's ID
	if( 'fld1234567' !== $field[ 'ID' ] ){
		//CHANGE ids (or slugs) of category(s) to exclude
		$args[ 'category__not_in' ] = array( '42' );
	}

	return $args;

});

only-category.php

<?php
/**
 * Limit Caldera Forms post type select to specific categories.
 */
add_filter( 'caldera_forms_autopopulate_post_type_args', function( $args, $field ) {

	//IMPORTANT change this to match your field's ID
	if( 'fld1234567' !== $field[ 'ID' ] ){
		//CHANGE ids (or slugs) of categories to include
		$args[ 'cat' ] = array( '2,6,17,38' );
	}

	return $args;

});