I understood that assuming no permission was granted for the alterations then the person doing the alterations can be held liable for the restitution, the Strata is reasponsible for the repairs but they can bill the owner for the cost.
The exception to this is if the current owner is not the owner who did the alteration and in this case it is totally a Strata cost.
For example if an owner decided that a common property structure needed demolishing and then went ahead and demolished it would you expect the Strata to pay for the rebuilding, I know who I’ve make pay the bill.