This is quite straightforward using an Outlook macro e.g.
Sub ChangeSubjectThenForward()
Dim olFolder As Folder
Dim oItem As Object
Dim olMsg As MailItem
Set olFolder = Session.GetDefaultFolder(olFolderInbox).folders("output") 'note the folder name is case sensitive!
For Each oItem In olFolder.Items
If TypeName(oItem) = "MailItem" Then
oItem.Subject = "The New Subject"
oItem.Save
Set olMsg = oItem.Forward
olMsg.Recipients.Add "someone@somewhere.com" 'the address of the person you are forwarding to
olMsg.Send
End If
Next oItem
lbl_Exit:
Set olFolder = Nothing
Set oItem = Nothing
Set olMsg = Nothing
Exit Sub
End Sub