In the third mission of the Modern Times campaign, I get the objective to export gold, yet, since my strategy always is start with boat loads of mines, I already mined ALL the gold on the island, so I have nothing left to export. Is there a way to still finish the objective or do I have to restart?
I do believe it would be possible to import some gold, then switch back to exporting that gold. But you'll be losing a lot of money in the process and it won't be easy.
I'd suggest restarting, really. I don't like it either, but you sometimes find better ways to do things by rebuilding :-)