qqline connects the first and third quartiles. How do I draw a line between different quantiles (ie 30% and 70%)?

Question

I have a qqnorm plot of a data set with 1000+ points. I want to draw a line between two quantiles at a time (say 30% and 70%) just as qqline does with 25% and 75%, but with

Answer 1

Make a new function by copying the code and changing the second line to:

x <- qnorm(c(0.30, 0.70))