The shirt editing seems to be much more limited in WE7. Less design options, less colors to choose from. A bit disappointing, overall.
I can't imagine the editing is as poor as it is. I was hoping you could buy additional editing options via the WE shop, but that doesn't look to be the case.
That being said, you should be able to move back and forth between the default shirts and the editing template with relative ease. I don't have a translation menu handy, but that is possible. You can't "lose" the default kits.
If you're looking to change Ajax, specifically, I would recommend leaving the default home kit. It's not possible to edit the home shirt so it looks any better. You can, however, edit the away kit to make it approximate the real life one better.
Best advice, though: wait for a patch. This'll be sorted out soon.