Here is the implemented code I used. I eventually had to run it from Excel as my administrator has disabled Outlook macros. Much of the code is from another source that I will credit when I can find the resource again.
If you can write vba in Outlook then just change this line below;
Set OutlookApp = New Outlook.Application
Sub OutlookAutoCorrector()
Dim msg As Outlook.MailItem
Dim OutlookApp As Outlook.Application
Dim insp As Outlook.Inspector
Dim strInput As String
Dim oRng As Range
Dim i As Long
Set OutlookApp = New Outlook.Application
Set insp = OutlookApp.Application.ActiveInspector
If insp.CurrentItem.Class = olMail Then
Set msg = insp.CurrentItem
If insp.EditorType = olEditorHTML Then ' outlook 2003
Set hed = msg.GetInspector.HTMLEditor
Set rng = hed.Selection.createRange
rng.pasteHTML "<b><font style='color: blue; background: yellow; font-size: 14pt;'>" & rng.Text & "</font></b>"
End If
If insp.EditorType = olEditorWord Then ' outlook 2013
Set hed = msg.GetInspector.WordEditor
Set appWord = hed.Application
Set rng = appWord.Selection '.MoveRight(Unit:=wdCharacter, Count:=1, Extend:=wdMove)
strInput = InputBox("Autocorrect Macro: replace ==>" & rng, "Autocorrect Word Replace", "Enter replacement HERE")
If strInput <> vbNullString Then
appWord.AutoCorrect.entries.Add Name:=rng, Value:=strInput
rng.collapse direction:=wdCollapseEnd 'UNTESTED, but something like this...
Else
MsgBox "Auto Correct Msgbox was closed. Try again."
End If
End If
End If
Set appWord = Nothing
Set insp = Nothing
Set rng = Nothing
Set hed = Nothing
Set msg = Nothing
End Sub