One thing for certain, it DOES NOT all even out at the end of the year. The extra time you spent and did not bill is GONE! As is the money you did not receive. Your time is valuable, don't waste it. That said any deviation from a standard light fixture installation (such as you have described) should be brought to the customers attention and explained that it will be more time and of course more money. My other thought would be modifying a fixture may cause UL listing trouble.
