Sure put a character style on the image you want to preserve the size of as you paste it in. Then assuming you have set up a character style called Preserve, you can have code like.
Sub PicSize_ALL_17cm()
Dim š As InlineShape
Dim Aspect As Double
For Each š In ActiveDocument.InlineShapes
if s.Range.Style <> "Preserve" then
Aspect = š.Width / š.Height
If (š.Width > CentimetersToPoints(11)) Then
š.Width = CentimetersToPoints(11)
š.Height = š.Width / Aspect
End If
End If
Next š
End Sub