Question: Can treasure fleet be casted upon a war fleet and when you instant travel to a port you dont gain danger.

that could be a major help if it can,right

yes you can Dracula

Indeed you can : some cast it on a war-fleet which has gained danger in attacks : then set it on a trade route : this means it can earn gold while the danger ticks down as, with TF on, it doesnt wait for the danger to drop to 1 before moving but nor does it gain any on port entry. Given a TF gives you 72 hours of trading in this way, its much more helpful than leaving the fleet sitting in port. It can still be hit, but will earn back far more than any plunder lost from such defences.