Text Variables and Scripts

I have a number of standard documents that a setup script uses. In each document there are text variables called Author and Job Number.

I'm working in VB and these commands can display the name and index of the variable but can't seem to find the way to actually change the value of the variable.

Set IDoc = InD.ActiveDocument
MsgBox IDoc.TextVariables("Author").Name
MsgBox IDoc.TextVariables("Author").Index

Any help would be much appreciated.