AFAIK in league you can’t add any units to China or to France with a bid, and you can only add units to territories or Sea Zones that already have units.
The Chinese bid is perfectly legal in the Global `40 league (unless it just changed). Strictly speaking it is also legal to bid Chinese units which they cannot buy in the normal course of a game, but that probably will be changed if it hasn’t already. There has been plenty of discussion on that topic.
Placing a French bid in Paris should also be perfectly legal. I don’t think doing so would be that helpful since at best maybe you’ve delayed the German attack on S. France or Normandy by one turn, which i don’t see as having a lot of strategic impact on German play.
A: 12
B: 11
A: 10
B: ok you get it, I get axis and you get allies at 10.
Going up
A: 8
B: OK, I take it at 8.
The difference with going up is you bid for what the other person will get as the allies. When you go down it is for what you want to take the allies with.