Can a builder who got permission from the panchayat to develop a layout in 1991, legally change the size of roads in the layout without the consent of the plot owners after selling all plots in 2006, even though the approval number remains the same?

No, a builder cannot unilaterally change the size of roads in a layout after selling plots, even if the initial permission from the panchayat remains valid. This would violate the rights of the plot owners and constitute a breach of contract, potentially leading to legal action.