Are my prayers valid after shifting from the obligation of washing dog impurity seven times to the view that washing it once or until its traces are removed is sufficient?

It is forbidden to switch between fatwas if it is done out of a pursuit of concessions and whims; indeed, following concessions is considered heresy or close to it. As for the cases in which it is permissible to switch from one fatwa to another, they are: if it becomes clear to the Muslim that the Sunnah is contrary to what he has acted upon, or if he asks a scholar who is more knowledgeable and trustworthy, or for an excuse such as extreme hardship. As for the impurity of a dog, it must be washed seven times, one of them with earth, and there is no difference between its licking or any part of its body, whether it touches a vessel, clothes, or the body.