Is the line “But get thee back; my soul is too much charged with blood of thine already”, a personification, a metaphor or neither?
This line contains several figures of speech. It's important to note a line may contain several figures of speech and they can overlap. For example, "He had an appetite like Henry VIII." This line contains a simile ( like Henry VIII) and an allusion to a historical figure who was known for his large appetite. The words, " my soul is too much charged" is an example of personification because it attributes something ethereal ( the human soul ) to something human. In addition, "my soul" is also an example of metonymy because the soul represents the entire person of Macbeth. "Blood of thine" is method of referring to having slain Macduff's family so it is a metaphor. "Blood" is also an example of metonymy because it represents McDuff's family.
It's a personification (which is, anyway, a form of metaphor) and a metonymy at the same time. The personification is of Macbeth's 'soul' as someone charged (in the legal sense) with a crime: and of course, must therefore be a metonymy (the part standing for the whole), as the criminal (metaphorically) 'charged' with these crimes is Macbeth.
'Blood of thine' is also a metaphor (and potentially a metonymy) - the 'blood' stands for bloodlines, and therefore Macduff's family (the play as a whole makes a strong link between blood - the substance- and bloodline).
It's complex - but I think mainly because Shakespeare had no name for these terms when he used them: he just used them!