I played a game with the Sophons and at the end of the game, I've unlocked the technology that allow trade. For the settlements I said that I must have the "mushrooms" (+50 science) to build it... but I didn't see that I had no mushrooms and I can't change it. Is there any bug or is it normal ? 

That's not Trade, that's colony development, but no, I don't think it's possible to change your choice.

Okay thanks