MB Relationships + MB Frontend Submission

Are there any ways to filter out the "add new" option? I'm using it in a shortcode with multiple custom field groups.

So, it seems you can target the relationship meta box as a normal field group using the same ID as in the form shortcode:

<?php
add_action( "rwmb_before_REL_ID_relationships_to", function( $meta_box ) {
    echo '<div id="customID">';
} );
add_action( "rwmb_after_REL_ID_relationships_to", function( $meta_box ) {
    echo '</div>';
} );

Maybe you can do something similar with validate hooks to change the "add new" option?
Or as a last resort, give the container ID above and target it with CSS #customID .addnew-class { display: none; }

Note this hook is after/within the .rwmb-meta-box container -- which doesn't help my case, since that's the div I was trying to hook into.

I have a really nice, orderly frontend form with tabs. Then at the end ... some select (relationship) fields which I can't control the labels or width of 🙃

Suggestion
Ideally a relationship field would work with any MB post/term/user field.

Then just like the "Set as parent" option, there could be a "Set relationship" option. It would also need to input/select a relationship ID. On save, the current editing object would have the applicable relationships updated.

I nearly set up several tax_advanced/user/post fields for my case. Then on-save I would need to check that relationship every time, check/delete all existing relationships (looping through them since there's no function to delete all), and set the new relationships according to field input.

I think it can work....but for now I'm just using the somewhat-random fields at the end of my form.

Hopefully the devs consider this 🙏 because it would be awesome to manage relationships anywhere within a form/field group, plus control metabox attributes, CSS ID, columns etc.