What right does an executive committee have to authorise an addition to common property?
If there is an MDU Agreement in place I don’t think it would be worth the paper it was written on unless approved by a special resolution at a general meeting.
IMO the short answer to your question is, unless any of the installations were approved via a special resolution, the owners corporation would have the right to reinstate common property to its former state (i.e. remove any unauthorised installations on common property).