Well basically what happened is that I wanted to reduce lag in my game so I though deleting neighbourhoods will solve the problem. But then I kind of wanted some of the prebuilt houses in RBH. So if I reinstall seasons. I will get the neighbourhood back? Note that I also installed Celebration and H&M Fashion so I am scared my saves will be corrupt.

I have reinstalled seasons and I got the RBH neighbourhood back with all default houses. After that I reimported the backed-up neighbourhood I was playing and renamed it. It seems to work ok.

You could just delete the neighborhood folder and it will delete all the neighborhoods without reinstalling and the game will automatically remake the folder and it will be just like you reinstalled. Theres a tutorial at modthesims2.com under technical help.