I have worked on plenty of cars in my time...thank you very much. (Especially in the early 90s most of the cars and trucks were from the mid to late 80s.) I have swapped out carbs, changed heads / valve gaskets, etc., and completely changed entire brake systems. (Master cylinder, drums / rotors, etc.)
Let me explain a little more about why I would not do this particular job myself. First, I no longer have access to the tools and equipment I once did. Sure, this isnt an extremely complex job, but it isnt an oil change either. Second, there is a value of my time factor. Considering that the Mazda techs are taking between 1.5 2.5 hours to do this job (with all the proper tools in the proper environment), I would assume I would need about 3 hours to do it. Three hours of my free time is worth way more than $160 to me. Finally, I have know way too many guys who have modded cars themselves, only to have it come back and bite them in the ass when something goes wrong. Even if the mods were done right, these guys would always have to revert their cars to stock before taking them to the dealer. (Or risk getting caught with a modded engine. The rumor was the dealers would tag your car somehow as modded. I dont knowbut that is what they said.) I knew a guy who pulled his turbo / tuner box out of his Integra no less than 5 times. Granted, that is an extreme case, but I would rather pay $160 and be 100% sure my warranty is intact.
Why take the risk a warranty and 3 hours of my time for $160. You said yourself that I wasnt going to be splitting any atoms, so how much could I really stand to learn on this particular task?