What aspects will need to be adjusted in the mapping for doing a turbo upgrade?

have got a 98 mx5 1.8 of which I've mapped and balanced up with a td04-13t at 1.1bar. Now I have everything homed in I'm considering a mild turbo upgrade for the td04-19t. What aspects of mapping and boost control will I need to think to rebalance back in on the tune from this mild upgrade to the exhaust turbine?

You're likely to find that the VE of the engine will improve so you'll need to increase the fuel delivery to maintain the same AFR. At the same time a reduction in turbine inlet pressure usually allows for a little more ignition advance. In terms of boost control I'd suggest you start at by disabling electronic boost control and tune at the wastegate spring pressure level. From here I'd then reduce your duty cycles by 10-15%, re-enable the boost control and tune from there - This should start with your boost safely below your existing tune.