lcMethodCustom(
  response,
  fun,
  center = meanNA,
  time = getOption("latrend.time"),
  id = getOption("latrend.id"),
  name = "custom"
)

data(latrendData)
# Stratification based on the mean response level
clusfun <- function(data, response, id, time, ...) {
   clusters <- data.table::as.data.table(data)[, mean(Y) > 0, by = Id]$V1
   lcModelCustom(data = data,
     trajectoryAssignments = factor(clusters, levels = c(FALSE, TRUE), labels = c("Low", "High")),
     response = response,
     time = time,
     id = id)
}
method <- lcMethodCustom(response = "Y", fun = clusfun, id = "Id", time = "Time")
model <- latrend(method, data = latrendData)