What biblical (scriptural) basis does a Christian have to command the blessings?

The closest verse i can think of is Isaiah 45:11 " Thus saith the LORD, the Holy One of Israel, and his Maker, Ask me of things to come concerning my sons, and concerning the work of my hands command ye me".

The "command your morning" scripture is actually based on Job 38:12-13:

"Have you ever given orders to the morning, or shown the dawn its place, that it might take the earth by the edges and shake the wicked out of it?"

Note that some versions like the KJV use "commanded" instead of "given orders to". You can judge for yourself if this is a sufficient basis for this belief.

The book of Job is where it is found. Job is the one who's speaking. He asked one of his friends if he commanded the morning to line up with God's word.

The basis for the "command the blessings" belief is through a sort of "literal and no-exceptions" interpretation of passages like these:

Matthew 7:7-8 ESV Ask, and it will be given to you; seek, and you will find; knock, and it will be opened to you. For everyone who asks receives, and the one who seeks finds, and to the one who knocks it will be opened.

John 14:13 ESV Whatever you ask in my name, this I will do, that the Father may be glorified in the Son.

John 16:23-24 ESV In that day you will ask nothing of me. Truly, truly, I say to you, whatever you ask of the Father in my name, he will give it to you. Until now you have asked nothing in my name. Ask, and you will receive, that your joy may be full.

Matthew 21:21-22 ESV And Jesus answered them, “Truly, I say to you, if you have faith and do not doubt, you will not only do what has been done to the fig tree, but even if you say to this mountain, ‘Be taken up and thrown into the sea,’ it will happen. And whatever you ask in prayer, you will receive, if you have faith.”

EXTRA: While out of the scope of your question, it's worth saying that the "command your blessings" belief is just another version of "name it, claim it", which more or less treats God like he is a genie from a magic lamp. It's important to append the above passages to ones like this:

James 4:1-3 ESV What causes quarrels and what causes fights among you? Is it not this, that your passions are at war within you? You desire and do not have, so you murder. You covet and cannot obtain, so you fight and quarrel. You do not have, because you do not ask. You ask and do not receive, because you ask wrongly, to spend it on your passions.

The commanding the morning and commanding God teachings are set in word of faith doctrine and most definitely not Biblical and by that I mean that they are a distortion of scripture. Job 38:12 God is asking Job the question have you commanded the morning since your days began or shown the Dawn its place. God is making a point and addressing Job's arrogance; Job had lived to see many mornings but never had the power to command one. What God is asking Job is did you create the sun and appoint the order of succession of day and night. If we read the book of Job we get the true meaning of this verse that is so blatantly torn out of its original context. Several teachers and preachers seem to believe this doctrine which however if researched and lined up with scripture is seen to be false and more in line with mysticism and new age beliefs.

There is none to support commanding our God to do anything. Would you walk into court and command a judge to reduce your sentence? Absolutely not, you would ask respectfully and explain your circumstance.

The same would go for your fleshly father. If you needed something all you have to do is ask respectfully. What father wouldn't give his children something they needed? How much more so our heavenly father. This is demonstrated by Jesus at Luke 11:11-13:

"Indeed, which father among you, if his son asks for a fish, will hand him a serpent instead of a fish?12 Or if he also asks for an egg, will hand him a scorpion? 13 Therefore, if you, although being wicked, know how to give good gifts to your children, how much more so will the Father in heaven give holy spirit to those asking him!”

Then at Matthew 6:32

"For all these are the things the nations are eagerly pursuing. Your heavenly Father knows that you need all these things."

So we see that God knows what we need and is eager to give it to us when we ask. If we want to show our love for god we show "fear" or respect for him. This means asking and not demanding. When we command something to happen, it is as if by our own hands or power we can make it happen. When we do that we take away from the glory of our father. Look at the example made of Moses when he didn't glorify god at numbers 20:10. We don't want to take the credit for something god does. We show humility and meekness by just asking and those are qualities God finds very favorable.

One passage often used to defend this doctrine is the words of Jesus in Mark 11:23-24:

“Truly I tell you, if anyone says to this mountain, ‘Go, throw yourself into the sea,’ and does not doubt in their heart but believes that what they say will happen, it will be done for them. Therefore I tell you, whatever you ask for in prayer, believe that you have received it, and it will be yours."