Do the Awliya' (pious people) perform Karamahs (extraordinary events caused by Allah for or through a pious person)?
Can they change anything in the heavens or on earth? Do they intercede with Allah for others while they are in Barzakh (period between death and the Resurrection) or not?
is an extraordinary event which Allah (Exalted be He) bestows on a pious person as an honor to protect him against harm, benefit him, or help him defend people's rights. But a pious person cannot perform these events whenever he wishes just as the prophet could not perform miracles by himself whenever he wished. It is Allah Alone Who helps them to do all these things. Allah (Exalted be He) says:
And they say: "Why are not signs sent down to him from his Lord? Say: "The signs are only with Allâh, and I am only a plain warner."
Also pious people are not empowered with any superiority to change things in the heavens or on earth except for what Allah enables them just like all other humans. They can make changes in things like farming, building, trading, and such works which ordinary humans do (Part No. 1; Page No. 575) with Allah's Will. In Barzakh, pious people cannot intercede for anyone whether alive or dead, as Allah (Exalted be He) says:
Say: “To Allâh belongs all intercession."
Allah also says:
And those whom they invoke instead of Him have no power of intercession - except for those who bear witness to the truth knowingly (i.e. believed in the Oneness of Allâh, and obeyed His Orders), and they know (the facts about the Oneness of Allâh).
Moreover, He says:
Who is he that can intercede with Him except with His Permission
Whoever believes that pious people govern the universe or that they know the Ghayb (Unseen), is a Kafir (disbeliever), as Allah (Glorified and Exalted be He) says:
To Allâh belongs the dominion of the heavens and the earth and all that is therein, and He is Able to do all things.
Also Allah (Glorified be He) says:
Say: “None in the heavens and the earth knows the Ghaib (Unseen) except Allâh”
Allah (Glorified be He) removes all ambiguity whatsoever and declares the truth in a clear-cut manner when addressing the Prophet (peace be upon him):
Say (O Muhammad صلى الله عليه وسلم): "I possess no power over benefit or harm to myself except as Allâh wills. If I had the knowledge of the Ghaib (Unseen), I should have secured for myself an abundance of wealth, and no evil should have touched me. I am but a warner, and a bringer of glad tidings unto people who believe."
May Allah grant us success. May peace and blessings be upon our Prophet Muhammad, his family, and Companions.