Electrical lighting question

[dandyfop]

I picked up a second hand possibly coralife (looks like one, but no tag) fixture that is 4 x 36w PC.

Now, I would prefer to have it be 2 x 72w, as the cost of bulbs would go way down.

The unit has two ballasts, with 4 pairs of wires coming out of each, 2 pairs for each PC.

Can I connect the pairs together to only have 2 pairs, and only two lights, if the total load in wattage is the same? Does a ballast really know if it has 2 36w bulbs, or 1 72w? And if so, which pairs would connect together, or does it matter?