Is it safe to change a hot water heater from propane to natural gas?

depending on the age of the water heater and the original application it is yes a easy orifice change out. on the mobile home type units they come setup ready to plumb LPG (propane) and come with the orifice to use natural gas. the orifice is located on main burner inside of the unit. on the new sealed combustion chamber water heaters you have to change out the gas control AND the orifice to go from lpg to natural gas or vice versa