This has been my exact experience in Manhattan, where a 3 Bed apartment got converted into 5 Bed. After we refused to pay additional rent. Interestingly in Mumbai my apartment building (a Co-op where we own) decided to demolish / rebuild and reduce the playground associated with the building. This allowed us to raze the 6 storey building built in 1960 into a 12 storied one. As a result, we now have an apartment in the same co-op with equivalent sq. footage and were paid additional money plus rent while the building was being rebuilt. Since it was a Co-op we could shop around for a developer who offered us the best deal. The current building will at least sustain till another 50 years. I have never found this happening in US. Since either the building did not have enough free space to expand upon adjacent to them or restriction on height increase.