General Plan Changed: In a move that will allow construction of several low-cost apartments for the elderly, the City Council has approved General Plan amendments and zone changes to permit a mixed commercial and residential development downtown. The project, unanimously endorsed in a second reading before the council Tuesday, will incorporate a bank building with new office suites, underground parking and 15 apartments in a single, four-level complex at Broadway and Beach Street. The developer, First American Bank and Trust Co. of Laguna Beach, will submit plans to city planners for approval this week. The 15 one-bedroom and studio apartments would be reserved for elderly tenants at rents between $400 and $600 a month. Coastal Commission approval is still required for the project before building can get under way, but Morris Skenderian, the architect, said work could begin as early as next February.