[Q] change rom without knox problems topic

hey guys,
what's up ?
i just bought a galaxy s6 edge(sm-g925i) and it came with a branded rom,
i'm from brasil and i bought on claro store, so, it came with the zta rom
i would like to know if i can change it to the zto rom without voiding my warranty and not triggering the knox counter, and how would i do this things.
i'm sorry about my bad english.

thanks :D;)