Add a group to a module
<?xml version="1.0"?>
<objects>
<object type="ModuleGroup">
<id_module>274</id_module>
<id_shop>1</id_shop>
<id_group>4</id_group>
</object>
</objects>
It also posible to delete this link:
<?xml version="1.0"?>
<delete>
<object type="ModuleGroup">
<id_module>274</id_module>
<id_shop>3</id_shop>
<id_group>4</id_group>
</object>
</delete>