こんばんわ。
こちらでいかがでしょうか。
Sub Test()
Dim AllH, AllF, TitH, TitF, BdyH, BdyF, Br_F, S0, S1 As String
Dim SS As String
Dim I, Imax As Integer
Dim Tmp As Variant
AllH = "<div class=" & Chr(34) & "cntt"">"
AllF = "</div>"
TitH = "<h3>"
TitF = "</h3>"
BdyH = "<p>"
BdyF = "</p>"
Br_F = "<br />"
Tmp = Split(Range("A1"), vbLf)
Imax = UBound(Tmp)
Cells(2, 1) = AllH
For I = 0 To Imax
If Len(Tmp(I)) > 0 Then
If InStr(1, Tmp(I), "◆") > 0 Then
S0 = TitH
S1 = TitF
Else
S0 = BdyH
S1 = BdyF
If I < Imax Then
If Tmp(I + 1) <> "" Then S1 = Br_F
End If
If I > 0 Then
If InStr(1, Tmp(I - 1), Br_F) > 0 Then S0 = ""
End If
End If
Tmp(I) = S0 & Tmp(I) & S1
End If
Cells(I + 3, 1) = Tmp(I)
Next I
Cells(I + 3, 1) = AllF
Range(Cells(2, 1), Cells(I + 3, 1)).Copy
End Sub