Well, yes, you could do that quite simply with a macro like:
Code:
Sub Demo()
ActiveDocument.Range.ParagraphFormat.Alignment = wdAlignParagraphJustifyLow
End Sub
or you could apply it to selected paragraphs with a macro like:
Code:
Sub Demo()
Selection.Range.ParagraphFormat.Alignment = wdAlignParagraphJustifyHi
End Sub
As I said, though, I haven't tried the JustifyHi/Low/Med options, so I can't tell you what they do.
For PC macro installation & usage instructions, see:
Installing Macros
For Mac macro installation & usage instructions, see:
https://wordmvp.com/Mac/InstallMacro.html