This probably violates some programming best practices for being too verbose but I find it to be effective and easy to understand.
nmesRAW$beltuse[nmesRAW$beltuse == 1] <- "Rarely"
nmesRAW$beltuse[nmesRAW$beltuse == 2] <- "Sometimes"
nmesRAW$beltuse[nmesRAW$beltuse == 3] <- "Always"