SOLVED!
After some more searching and testing and hair pulling, I found a way to remap some of the fields on import from Rezi, our solution is below just in case anyone else has this/similar issue.
// Rename post name with property ref
add_action('propertyhive_property_imported_dezrez_json', 'append_postcode_to_display_address', 10, 2);
function append_postcode_to_display_address($post_id, $property)
{
$newDescription = '';
foreach ($property['Descriptions'] as $description) {
// Room Counts
if ($description['Name'] == 'Main Marketing') {
$newDescription = $description['Text'];
}
}
$my_post = array(
'ID' => $post_id,
'post_name' => $property['RoleId'],
'post_content' => $newDescription,
);
// Update the post into the database
$post_id = wp_update_post($my_post);
}