Here is a heavy-handed approach to reformat the output (which also loses information contained in the original notation):
library(tidyverse)
set.seed(1234)
d <- data.frame(int_var = sample.int(50, 50))
d %>%
mutate(group_var = cut(int_var, breaks = c(0, 10, 20, 30, 40, 50)),
group_var_temp = gsub(pattern = "\\(|\\[|\\)|\\]", replacement = "", group_var)) %>%
separate(col = group_var_temp, into = c("lwr", "upr")) %>%
mutate(group_var_new = paste(lwr, upr, sep = " - "))
There is likely a more concise way to write the regex in the gsub, but as a regex novice I find that pattern intuitive (i.e., separately escape \\ each bracket type and combine with |).