Bermaz already made it clear changing the transmission fluid will void warranty, and i doubt any SC would perform it while keeping the warranty since it goes against their policy (unless you found a lobang with the sc manager lah)

there's 2 recommendations -

1) You proceed to change the fluid at outside workshop @ 20k or whatever mileage, but you take the risk of voiding your warranty and incase touchwood your gearbox really have any issues before 5 years or 100k km, you are gonna incur a greater loss of replacing / fixing the gearbox

or 2) Keep the gearbox as it is within the warranty period, since its covered by warranty anything happen just claim it. Once warranty over you may proceed to change the fluid