My understanding is the the random forest picks randomly mtry variables to build each decision tree. So if mtry=ncol/3 then each variables will be used on average in 1/3 of the trees. And 2/3 of the trees will not use them.
But what if I know that a single variable is probably very important, would it be good to manually increase the probability that this variable be picked in each tree? Is it feasible with the randomForest package in R?