That gets done for every company around the country that might want to leave a state. The incentives are usually tied to the number of employees and there is no doubt Carrier could have gotten these incentives anytime over the last 2 years. But once Trump won they will see a drastic cut in taxes.
If you're talking about corporate income taxes Carrier will get the new rates whether they offshore some production or not.
The US taxes their net income in the US regardless of where their factories are.