What is the ruling on changing the intention of a prayer after completing it, and must the prayers whose intention was changed be repeated, or do they remain obligatory?

Whoever performs the obligatory prayer with a sound intention has fulfilled their obligation, and they cannot convert it into a supererogatory prayer after completing it. Changing the intention from an obligatory prayer to a supererogatory prayer after finishing the prayer does not affect its validity, but changing it during the prayer invalidates it.