I'm not sure what customs you are referring too as the HRE had little to no Roman customs in it besides the title of Kaiser (which is taken from Caesar), it doesn't help that while the Byzantine empire is quite literally the Roman Empire and not some successor state (while they were more Greek than Roman they still saw themselves as Romans) the HRE wasn't created until around 500 odd years later with the crowning of Otto I, it's hard to have a claim as a successor to the West Roman Empire when you show up 500 years late and have little in common with the Roman Empire.