How will semi slicks make a difference to brake heat? Ok, so they grip the road more, but you still have to effectively shed the same inertial energy, which gets turned into heat shed from the brake system.
CS front brakes aren't any different to the PP/R ones are they?
Even if they are, again, probably more logically swap the fluid, lines and pads first - because you'll be needing these for a big brake kit anyway.
I don't think those mods will affect the warranty anyway - well, apart from no warranty on pads and brake lines, which are unlikely fail points anyway.