Have to change fluid when swap rotors/pads?
 

2009 with almost 50k, Changing pads and rotors too, leaving lines alone. Do I have to change fluid?

I would... Go GTR fluid, helps with brake fade.
I THINK Nissan recommends brake fluid flush every 30k or some BS because it absorbs water from the air which does something and it makes the pads not last as long, and yada yada...

Just make sure you don't get raped for a liter of fluid, The Nismo Shop (West Covina Nissan sells it for $30 Nissan Factory OEM GT-R Special DOT 4 Brake Fluid KN9U0-40001P - Nissan R35 GT-R)

you don't have to, but you should.

After 3 years of DD it will be a bit yucky but still functional. You preserve the life of expensive components (such as ABS controllers) by flushing every 2-3 years on a street only car. Don't drive hard? Then don't waste money on expensive fluid, 32 oz bottle of Vavoline for $8 will do you just fine.

The higher the boiling temp, the more hygroscopic the brake fluid is, as a good rule of thumb. (Note, products like SRF are exceptions) so for a DD I usually suggest just simple auto parts fluid that meets the DOT4 specification. Industry standard is to flush the fluid every 2 years regardless of mileage.

-Your Pal
Fishey

As per Mike, you shouldn't have/need to change it, but, as long as you're there, I'd go ahead and flush/replace.
When in doubt, use new stuff (this applies to most vehicle fluids, especially lubricants) - it's not that expensive. Do you really want to scrimp on such a nice car? ;)