Just FYI transmission fluid doesn't break down, however it does get dirty. The seals do breakdown eventually and need replacing.
Yes, it does break down.
I usually change mine every year, although, I believe Mazda recommends it only every 96k.
I tired Redline MTL and MT90. Did not like either fluid.
Then I tried Motul Gear 300. WOW! Much better than stock or either Redline fluid.
there is no specific mazda guideline. at least not from mazda canada.
with that said we check on any car over 75xxx km. its an always anytime we replace an axle, or do a clutch.