Feel free to use storebought black sesame paste if you’d prefer to skip the hassle of making your own.
If you don’t have yuanyang mix, you can use instant milk tea mix instead, or make your own yuanyang by combining instant espresso powder with black tea powder. If you only have tea bags or tea leaves, you can infuse the milk by steeping the tea in it before using it in the glaze.
The rolls can be frozen at various points. You can freeze the unbaked rolls just after shaping and before the second rise; when ready to bake, let the rolls thaw overnight in the refrigerator and then let them proof at room temperature before baking as normal. Alternatively, you can place the still-frozen rolls in a cold oven while it preheats and bake as normal after it reaches the preheated temperature, keeping an eye on the browning. It may take a little less time to bake (and will expand less than if allowed to come to room temperature more slowly). You can also freeze the baked rolls, unglazed, by wrapping tightly in foil once cool. To reheat, just microwave from frozen for 30 seconds, or bake from frozen in a preheated oven at 350° F for 10-15 minutes.