Any ideas on how to import a new PNG in the editor so I can use it on PS3?
Just do as I said before. Use league structure in the editor and switch the team you want to edit kits on with a real team, just be sure to choose a team in a non-licensed league, as team edit will freeze in a licensed league. I choosed a team in D2 league and it went well.
After that go on PS3 and edit your team. After that you can switch teams again with the editor how you want.
Myself switched the whole D2 league with hidden teams beginning at the top of the list. There are 38 teams in the list but it is only the bottom four the will appear IG. From those four teams even the players show up in the edit mode IG if you have transfered already IG players with the fake players. The fake players on those teams can't be found using search function in IG. But if you assign them to teams they will be there just as if you don't apply transfers after downloading DLC when players is supposed to dissapear.
That being said, I do as this with the hidden teams to get them useful. Switch teams in the editor, edit team as you want and after that start ML and save just team data. This makes the team you have edited playable through exhibition games even if you have switched back in the editor after that!
This became a long post but hope you understand my point with it!