I'm going with "scalable". I don't think I was looking at all at spirit/letter of the law at all; just on how the gospel has appeared over various dispensations.
To me, flexible sounds a little too convenient. That being said, I do think things can alter depending on the people and situations. Vort brought up the letter vs spirit. I look at the 10 Commandments and the rest of the Law of Moses as something of a simplified version of all that we should be doing. It's simpler and specific, but it did provide a great framework.
Scalable, to me, makes it sound like things adjust more than change and alter. The Law of Moses was the same principles we believe in, just scaled to the situation.
I know a lot of people complain about and leave the church over seeming changes to the gospel. Those that I have studied seem to maintain the same idea--only the details of how it was brought about our different. I see that as an adjustment.