Changes to the common property require to be approved by the OC (not the EC) and if it is an improvement (as opposed to repair) it needs a 75% majority to approve it. If the first DA was approved by the OC and the EC had delegated authority to implement it then if that DA is changed the whole process needs restarting and it needs to go back to the OC to be re approved by an EGM with a 75% majority.