how would this recipe for banana bread be modified for high altitude?!

I suspect that as long as you let batter sit for 20 minutes it should bake the same so long as other baking works at the set temperatures. I understand boiling and cooking in liquid temperatures need to be adjusted due to pressure ie boiling point of water is 100 or 212 on C and F scale at sea level but is changed as altitude increases but the temperature of an oven should be the same at any level.
Edit I discovered this on line and adjustments required for baking.

Muffins & Quick Breads

This category also includes scones, biscuits, and cornbread. For the correct rise at high altitude, baking powder or baking soda must be reduced slightly. Also, you get a better rise and quicker set with an acidic batter, so you can reduce some of the baking soda, which neutralizes acidity—don't omit all of it as some is needed for leavening. To strengthen batter and prevent collapse, sugar is reduced and flour increased. Extra liquid can be added (it is especially good to substitute buttermilk or yogurt for water or milk) to compensate for dry air and drier flour at altitude. Quick breads baked in loaf pans may crust over and start to brown on top before the batter underneath begins to set. To prevent this, sometimes it is helpful to cover the pan loosely with foil after half the baking time or to substitute a tube pan for a loaf pan. To get a better rise between 4,000 and 6,000 feet, increase oven temperature by 15°F to 25°F. At higher elevations, keep original heat and increase baking time slightly.

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