Like to know what you find out as well. I have a 2014 so more warranty left than you but I want to put a Roush S2 or Brenspeed 650R and weighing the same options as you for warranty vs non-warranty install.
2014 Mustang GT : 6spd manual, sterling gray
MODS : tint, Pioneer 4100nex, AMR staggered charcoal, gt500 axlebacks
Previous Mustang : 2006 Mustang GT, 5spd manual, windveil blue, black interior IUP, 18in fanblades, spoiler delete, 5/20 tint
MODS : sequential turns, CDC ducktail, AVIC-D3+reverse keycam, CDC chin spoiler, C&L CAI Brenspeed 93 tune, MAC axlebacks
Previous Mustang : 1967 Mustang Coupe, V8 289 auto, red with black interior