Regarding flipping a country contract cart to the general contract side, here are a couple of scenarios that I didn't find covered in the manual and had some questions about them.
1) User picks up a country contract card (3 cargo containers). Use a load action to load cargo onto a boat (1 cargo container). On the next turn decides that they no either no longer (or cannot) load the remaining 2 cargo containers. Can the user flip the country contract to the general contract side?
2) Same scenario as #1 except at the end of their first turn there is only 1 cargo contain left on the company contract. Can the user flip the country contract to the general contract side?
Players are free to examine both sides of the Contract cards before choosing them and use either side
This will help you decide if you want to use the front to get a flag or the back of the card if the original contract isn't the optimal move at that moment. By comparing the other sides of each contract card you can decide which one is best for your current situation (e.g., to clear out the warehouse to avoid paying high fees, or loading the rail table, etc.)
Once you place the dice on your contract card it is binding which means you can't use the generic contract side anymore as dkeisen said.