[R] Cost function in cv. glm for a fitted logistic model when cutoff value of the model is not 0.5

I have a logistic model fitted with the following R function: glmfit<-glm(formula, data, family=binomial) A reasonable cutoff value in order to get a good data classification (or confusion matrix) with the fitted model is 0.2 instead of the mostly used 0.5. And I want to use the `cv.glm` fu

[R] How can I use the predict function in R in a logistic regression fitted years ago?

I have a problem that I am trying to resolve with no success. More than two days searching and I didn't get a single clue. Sorry if the answer is out there and I didn't find it. Suppose that you have a logistic equation regression (binary model) from an old model that you estimated some years ago.