The simple solution to your concern about excess data roaming is to just download a few movies or other data heavy services prior to your trip during the billing cycle. This is usually a good plan anyway for flights or slow hotel WiFi. You are entitled to 5 Gb of free, high speed data so download 6+ Gb on your line while at home to avoid any conflict. You will then be exempt from the “51% Rule”, and in full compliance. From what I have heard, they don’t take any action for a few months of the data imbalance anyway.

I have mentioned that I have several vacant lines, so I can just switch to a different sim when the free 5Gb is depleted. This will also work for the excess roaming issue.