We contributed to font-awesome 5 (yea), and we are looking from moving from our existing icons (Symbol set) to font-awesome. Will the naming of icons and usage of font-awesome
It's not backwards compatible.
I just publish a script to do the migration from 4 to 5 in:
https://github.com/estebandelaf/scripts/blob/master/fontawesome4to5.sh
PS: I know the post is from a year ago, but is the second result in google for "fontawesome migration script 4 to 5".