Yes its easy, go to
settings/ shipping & delivery/ manage rates/ scroll to the rate you want to change/ click the 3 dots/ click edit rate.
now you see the page to edit rate page/ click in the rate name field and start typing
now you should see a (+add ) pop up, click it and your new name will be added!
Tip: I make the new name in word and copy/paste it back in as its hard to see in the window provided.
Hello, I've been trying to figure this out as well and found a loophole. All you have to do is select "Custom flat rate (no shipping time)" from the edit rate section. then change the title to Standard (4-6 business days) for example.
Hope this helps