Here is my 2 cents ..
Option 1 .. A seperate custom credit "account" that way all credits purchased can be used specifically for customization.
Option 2 .. Custom Packs.
Pack 1 gives you enough credits to change the team name/city and colors.
Pack 2 gives you enough credits for Pack 1 + changing uniforms and logos.
I would also suggest opening the window to customize all season versus just the opening portion of the season .. If possible
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On a personal note, being "snippy" about issues doesnt help the MFN Community at all. I try to think of a solution when I make a suggestion. It may not be practical or maybe others can provide better suggestions.
Also remember, this game can essentially be played for free. JDB works hard at it and to me, buying credits from time to time is my way of saying thank you.