The only default changes required for a universal app is:
Xcode / Configuration (Project) / Deployment (Setting) / Targeted Device Family = iPhone/iPad
and I some iPad screenshots in iTunes Connect.
If this is your case, it would be interesting to know if an app can be updated to universal.
I forgot to set this, but also I thought that any iphone app will work on iPad, and so they will be set by default. Sincerely, I see no sense in the need to set any (old) iOS 320x480 program to "work on iPad", as they will work on 2x zoom mode.
Well, I have update the xcode thing and sent to apple the new binaries.
Notice that I have 2 different updates:
-A 320x480 app (so, it really is not universal)
-A real universal app, that works in 320x480, 640x960 and 768x1024 resolution.
In a week we will have news.