Spiced rum

Measured by weight; approximate spirit density not needed.

Instead of Spiced rum

Dark rum
Use the same weight; stir in a pinch of ground cinnamon and ground clove and leave for 10 minutes before using.
Rum
Use the same weight; add the spice pinch and a little soft brown sugar if the recipe expects sweetness.
Brandy or rum
Use the same weight; brandy is fruitier and less sweet, so add a pinch of ground cinnamon.