I think you can overcome this with time. I used to be really neurotic about trying new things. But lately I have been trying new stuff every now and then and if I have had a day afterwards when things have been a bit worse than usual that still hasn't stopped me from trying the new stuff again after a few days and it has worked just fine meaning it probably wasn't the new food item that caused the problem.
But I think this is something that comes with time. I don't think you can make yourself think differently. You need to ease into it. I am doing the hypnotherapy program right now too so that is probably also part of the reason why I am more relaxed about these things. However I am still more careful when it's important to be well, like now before Xmas I am not trying any crazy things as it is really important to me to be able to go home and spend Xmas with my family.