I don't know of any way to do that without also changing the numbers into text. If that is acceptable, here are some examples.
x <- 1200000000
x
#> [1] 1.2e+09
format(x, scientific = FALSE)
#> [1] "1200000000"
format(x, scientific = FALSE, big.mark = ",")
#> [1] "1,200,000,000"
Created on 2020-05-20 by the reprex package (v0.3.0)
If you cannot use text, please explain what you are trying to accomplish.