functions.php

// assuming the non-standard meta key is `job_import_id` (this filter is for Admin Side)
add_filter( 'job_manager_visibility_permalink_get_field_value_job_import_id_is_hidden_meta', 'smyles_job_import_id_permalink_not_hidden' );

function smyles_job_import_id_permalink_not_hidden(){
    return false;
}

// This is for frontend handling
add_filter( 'job_manager_visibility_permalink_frontend_get_field_value_job_import_id', 'smyles_job_import_id_frontend', 10, 4 );

/**
 * Fontend Handling
 * 
 * @var $value          The value that is going to be returned and used for the permalink
 * @var $all_fields     All field configurations in array format
 * @var $values         All values in array format passed by core WP Job Manager plugin after validations
 * @var $field_value    Same as $value, unless unable to determine how to pull value, $value will be empty string and this will be the actual value
 * 
 * @return string
 */
function smyles_job_import_id_frontend( $value, $all_fields, $values, $field_value ){
    
    // It's up to you to return whatever value you want.  Mainly because if the value was submitted via the form
    // there would be no need to use this filter, as the plugin already handles it.  This filter would be used to
    // customize a value, or to return your own custom value.
    
    return 'somecustomvalue';
}