DR and BDR election

Does the DR and BDR change for each and every interface for which the OSPF has been advertised

Yes, a DR/BDR election is held on every broadcast interfaces. The result of the election on one interface has no impact on the election on the other interfaces.

The DR/BDR election occurs per OSPF process. If a router has two interfaces each running in different OSPF processes then each interface will participate in the DR/BDR election only in the OSPF process to which it belongs.

Sorry Losh, but DR/BDR election occurs per broadcast interfaces regardless to which OSPF process the interface belong to. If a router has two broadcast interfaces it will participate to two DR/BDR elections regardless to which process those interfaces belong.