def modify(self, symbol, base_value):
        """
        Change the base value of a unit symbol.  Useful for adjusting code
        units after parsing parameters.

        Parameters
        ----------

        symbol : str
           The name of the symbol to modify
        base_value : float
           The new base_value for the symbol.

        """
        self._unit_system_id = None

        if symbol not in self.lut:
            raise SymbolNotFoundError(
                "Tried to modify the symbol '%s', but it does not exist "
                "in this registry." % symbol
            )

        if hasattr(base_value, "in_base"):
            new_dimensions = base_value.units.dimensions
            base_value = base_value.in_base("mks")
            base_value = base_value.value
        else:
            new_dimensions = self.lut[symbol][1]

        self.lut[symbol] = (float(base_value), new_dimensions) + self.lut[symbol][2:]
Change the base value of a unit symbol.  Useful for adjusting code
        units after parsing parameters.

        Parameters
        ----------

        symbol : str
           The name of the symbol to modify
        base_value : float
           The new base_value for the symbol.