Change custom_post_name in admin

hoping someone can help me with a little plugin I made (I don’t normally do this) I needed to change a Custom Post Type slug in a theme so…

function custom_post_name () {
return array(
'feeds' => true,
'slug' => 'deals',
'with_front' => false,
);
}
add_filter( 'mb_project_posttype_rewrite_args', 'custom_post_name' );

This worked fine and I just need to change ‘deals’ to whatever I want then I am good to go. Problem is a few others have asked for this fix as well so I thought it would be nice if I could add an admin function where I could just have them add ‘deals’ or whatever they want to a textarea or something like that. Not sure how to do it though. Any help would be appreciated.