I'm not sure I understand what you want. You mention that you do get the "+Combat" and "-Combat" messages. Do you just want to change them to say "Entering Combat" and "Leaving Combat"? If so, you just need to open the "localization.lua" file in the sct folder and find lines 25 and 26:
Code:
SCT.LOCALS.Combat = "+Combat"; -- Message to be displayed when entering combat
SCT.LOCALS.NoCombat = "-Combat"; -- Message to be displayed when leaving combat
And change the messages to what you'd like them to say.
What you tried won't work because there's no "entering combat" message in the combat log.