How would you recommend going about changing fluid in a "lifetime" tranny? Specifically in a 2007…

How would you recommend going about changing fluid in a "lifetime" tranny? Specifically in a 2007 Toyota 4Runner sport edition V8. They say not too but I can't believe anything is lifetime... I'm definitely a DIY kinda guy..

And as always thank you for all your knowledge!!

 I would, it's complex normally, but if it never leaked out, just drain out the old fluid, measure how much came out, and put that same amount back in with new fluid
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