Hi Chaz.
Assuming the weather doesn't change you must begin the race on the tyres you selected for stint 1. The system locks down ten minutes before the race start to allow qualifying to happen. The push level, tyre compound and fuel load that are selected when lock down happens are how your cars will arrive on the grid. There is no option to manually change tyres on the grid.
The only exception to this is if the weather changes after lock down and before the race starts. If this happens, depending on how you've set your advanced strategy, you MIGHT start on different tyres to those you selected for stint 1. There is still no option to make these adjustments manually you have to take what the advanced strategy throws at you.
BTW, Michelin re-treads are a cheat, they're much too fast and long lasting :-)