Pope Pius X decreed that children did not have to wait until age 12 to receive the Eucharist. Can the canon law or Papal decrees ever be changed in the future to allow infants of children under the age of 7 to receive the Eucharist? Does the Pope have the power or authority to change these laws in the future or are they church pratices that can never be altered or dismissed?
The law of when first communion is to take place is a discipline, not a doctrine. The Latin Church has the tradition of waiting until the child can recognize the Eucharist as a sacrament before permitting reception. The Eastern Catholic Churches have an ancient unbroken tradition of giving communion to infants. The Latin Church could decide to change its practice/discipline to match the Eastern Catholic Churches or it could keep it as it is now. Its simply a matter of prudential judgment.
Since this is simply a matter of ecclesiastical law and not divine law, any Pope (as supreme legislator) can change or altar the age of first communion.