rings

Q: Is resizing of rings or other jewellery permissible in Islam? If so, does one have to pay zakat based on the original weight of the jewellery or the new reduced weight?

Q: Recently, I heard in a sermon that it is not permissible for us, Muslims to wear rings made of stone or some other material or taweez with the belief that it will avoid harm and it will give us the blessings and barakah. In my locality most of the imams follow the trend of wearing such rings or taweez. Is it permissible for me to do namaz behind them?