How to rotate a multiple objects by 180 deegrees referencing their own center point?
If tey are blocks...and their orientation is originally same angle, select blocks, go to properties, rotation, type in 180+ original angle. If they are not blocks... make them blocks with orientation 0 and then follow if blocks instruction.. I know process is pain in neck if a lot of various items are involved and/or they have various original angles but I just tested it and it works here.
Only arcs, circles and ellipses have center points. The chance of getting this question wrong is very high. The OP should clarify his intentions.
Sorry it will rotate about the block base point. he will have to redefine blocks as having their base point at their center.