Create a macro that searches for a case sensitive word and then changes the case for every word following it until another key character is found.

I think this macro will do what you're asking for.

Sub LabelCase()

    Dim rgSrch As Range
    Dim rgChg As Range
    Dim strLabel As String

    Set rgSrch = ActiveDocument.Range

    With rgSrch.Find
        .Text = "label " & Chr(34)
        .MatchCase = False
        While .Execute
            Set rgChg = rgSrch.Duplicate
            With rgChg
                .Collapse wdCollapseEnd
                ' extend range to next quote or paragraph mark,
                ' whichever comes first
                .MoveEndUntil Cset:=Chr(34) & Chr(13), Count:=wdForward
            End With

            Select Case Left(rgSrch.Text, 2)
                Case "La"   ' want title case
                    ' force change of all caps in mixed-case title
                    rgChg.Case = wdLowerCase
                    rgChg.Case = wdTitleWord
                Case "LA"   ' want all caps
                    rgChg.Case = wdUpperCase
                Case "la"   ' want all lower case
                    rgChg.Case = wdLowerCase
                Case Else   ' mistake -- do nothing
            End Select

            rgSrch.Collapse wdCollapseEnd
        Wend
    End With
End Sub

There are a couple of items to note:

• If the label that you want to change is missing the ending quote mark, a naive treatment would consider everything from the opening quote up to the quote after the next "Label" marker to be one big label. I've handled this by assuming that in such a case, the current label ends at the next paragraph mark.
• An oddity of the way Word applies the wdTitleWord case is that if the text in the range includes some words in all caps and other words in lower case or mixed case, then the all-caps words are left all-caps. To work around this, I've first changed the text to all-lower-case and then applied wdTitleWord.