If statement with pipe - r

Question

I've seen a few articles on how to use if statements or conditionals using piping, but I'm not sure how to apply it to my situation. Along with a specific answer to my problem, I was also hoping for also a more general explanation about adding a if statement with piping so I am able to handle most situations.
I tried to learn to use this answer below (use if() to use select() within a dplyr pipe chain), but I don't understand why we are supplying "." as an argument on the third line below and when I should do so
mtcars %>%
group_by(cyl) %>%
{ if (cond) filter(., am == 1) else . } %>%
summarise(m = mean(wt))
Here's a sample of my data:
df_parse<-
structure(list(value = c("HURESPLI\t2\tLINE NUMBER OF THE RESPONDENT\tCURRENT\t22 - 23",
"FILLER\t2\t\t27 - 28", "HUBUSL1\t2\tENTER LINE NUMBER\t81 - 82",
"GEDIV\t1\tDIVISION\t91 - 91", "GESTFIPS\t2\tFEDERAL INFORMATION\t93 - 94"
), starts_with_position = c(TRUE, TRUE, TRUE, TRUE, TRUE), missing_vars = c("HUFINAL\t FINAL OUTCOME CODE\t 24 - 26",
"HETENURE\t ARE YOUR LIVING QUARTERS... (READ ANSWER CATEGORIES)\t 29 - 30",
"FOR HUBUS = 1 VALID ENTRIES 83 - 84", " 92 - 92", " 95 - 95"
)), row.names = c(NA, 5L), class = "data.frame")
I'm trying to separate out the missing_vars column using extract (tidyr) and gsub as shown below:
df_parse<-
df_parse %>%
mutate(dup_value2 = missing_vars) %>%
extract(col = dup_value2, into = "position2", regex = "(\\d+\\s*-\\s*\\d+)$") %>%
mutate(id2 = gsub(pattern = "\\t.*", replacement = "", x = missing_vars)) %>%
mutate(desc2 = gsub(".*\\\t\\d+\\\t", replacement = "", x = missing_vars)) %>%
mutate(desc2 = gsub("(\\d+\\s*-\\s*\\d+)$", replacement = "", x = missing_vars))
This works fine, but I wanted to add a conditional on the start of this pipe, where df_parse$starts_with_position == TRUE
Something like this? (I know it doesn't work)
df_parse %>% if(starts_with_position==TRUE){
mutate(dup_value2 = missing_vars) %>%
extract(col = dup_value2, into = "position2", regex = "(\\d+\\s*-\\s*\\d+)$") %>%
mutate(id2 = gsub(pattern = "\\t.*", replacement = "", x = missing_vars)) %>%
mutate(desc2 = gsub(".*\\\t\\d+\\\t", replacement = "", x = missing_vars)) %>%
mutate(desc2 = gsub("(\\d+\\s*-\\s*\\d+)$", replacement = "", x = missing_vars))
}else ""