There are two options I can think of:
Option 1: Subscribing to the playlists on your other account. You can find your profile inside spotify by typing in 'spotify:user:username' in the Spotify search box. For example, if the username for your old account is 'ciscotopher' you would type in: 'spotify:user:ciscotopher'
Once you find your old profile you can subscribe to the playlists on your new account.
Note: If the old account were to be closed, the playlists wouldn't disappear. It would just be very hard to find them.
Option 2: You could make the playlist colaborative and share it with your new account so that you would be able to edit the playlist. Learn how by clicking here, or follow the steps outlined bellow.
If you have any other questions, please don't hesitate to ask :)
Your welcome, i'm glad it helped!
I would really appreciate if you could please click 'Accept as Solution' on my previous post to help others find the solution faster.