Things can get changed. With about 6 months of notice, the production order can be changed. The later it is changed, the higher costs involved. Getting the PW
engines early would be a big roadblock, but it is possible that for the right price that it can happen.
There are a few 777-200ER slots out there for Asiana and ANA. For an extra special customer like ANA, things can be done. Expediting fees can be made to suppliers. Other airlines are willing to trade slots. It’s virtually impossible for a new customer to get expedited delivery slots, but for an existing customer with the supply chain already setup for all the customer options, it can happen for the right price.
Trading slots around when high production is in demand is rare. However when there is a recession and financial credit crunch, airplanes get swapped all the time. In 2009 & 2010, customers were struggling to get financing and airlines were paying fees to push back deliveries. There was a lot of shuffling that happened.
If you have never designed an airplane part before, let the real designers do the work!