You can currently upload your own team graphic banner in the custom leagues, which is one of the premium features. I toyed around with player faces and that's something I'd like to do eventually, but it's something that's significantly down the priority list.

So on custom leagues you can upload a team helmet or logo?

Yes, custom leagues you can:

* Rename your team
* Change your team's city
* Upload your team's image
* Change your stadium information
* Change your team's colors

So your purchased credits will never go down unless you try and join multiple leagues in one day.

I think that's a better way of phrasing it unless I got the actual concept wrong.

Yes - your purchased credits will never go down unless you join or renew more than one team in a day, or use your credits to customize your team or players.