Note - this is for family premium and not individual. Usually the family premium trial is available for one month only.
Family members living under one roof can enjoy up to 6 Premium accounts. Try 3 months free, only $17.99/month after.
Offer not available to users who already tried Premium. Cancel anytime.
Steps to copy your existing playlist to a new account -
1) Make them public on your old account.
2) Sign into your new account.
3) Search for you old username.
4) When you find you old account and public playlist(s) copy all the songs into a new playlist(s).
Great find OP. Just in time to cancel the YouTube premium 3 month offer.
For anyone looking to also move from YouTube music free trial, I used this for my playlists - https://www.tunemymusic.com/ - worked a treat.