How might Shakespeare's relationship with King James I have influenced Macbeth?

King James I was a generous patron to Shakespeare, and his patronage resulted in Shakespeare's becoming quite wealthy. Because of this, Shakespeare tended to alter his source materials and insert references that flattered King James into many of his works.
The setting of the play and its use of medieval Scottish source material is connected to James' own Scottish heritage. Rather than treat, as the source material did, usurpation of a throne as a relatively ordinary occurrence of the period and Macbeth himself as a relatively decent ruler who killed his predecessor and was in turn murdered, Shakespeare emphasizes the legitimacy of Duncan's authority and the heinousness of Macbeth's rebellion against his rightful king. This emphasis on the legitimacy of kingship and the awful consequences of rebellion would obviously meet James' approval.
Finally, the play is deeply religious in focus, concerned witchcraft and filled with Biblical allusions, two key interests of King James. 
http://www.shakespeare-online.com/plays/macbeth/jamescompliments.html