Substituting oksusu-cha (Korean corn tea; you can use cheap stuff from any Asian grocery store) for the black tea and brown sugar syrup for the simple syrup makes for a subtle, complex, and delicious cocktail.
I've made this a few times, and each time, it seemed like something was missing; it was always a little bit one-note. Tonight, I tried adding a barspoon of Pernod anisette, and the hint of liquorice and bitterness harmonized surprisingly well with the Grand Marnier. This might become a regular for me.