OK

would it be ok if i get the headers/exhaust/turbo cermaic coated after i get a retune?

Or should it be done with them already coated?

Im not sure if the ceramic changes the dynamics, as it only increases exh temp more rapdily due to insulation.Thus increasing spool more sooner, as per taking some time to heat up.
Im planning tune to happen with the pipes/turbo ported btw