<<Can you tell me how to stop the Macro if the 'then' condition is met, and
continue if it isn't?

Leave the 'then' condition empty and have code in the 'else' part of the
clause only, or revise the logic as follows:

Sub Test()
If Range("Q44").Value < "Fill in..." And _
Range("F47").Value < Range("AB2").Value _
Then
'Your code here.
End If
End Sub

Except that your OP (original post) said:
<<IF new, then continue macro. IF unchanged, then display error...
--
Regards,
Bill Renaud