EDIT: I'm leaving my original answer below for conversations sake as there is good dialogue below. As @mja noted when you initially create an app ID it is associated with one of a few available prefixes to your developer portal and that prefix may be used by iOS to associate & differentiate between apps.
EDIT2: When I go into my Enterprise Portal and try to create an app ID with an identical value to an existing app ID but with a different prefix it still blows up on me and says:
An App ID with Identifier 'com.mycompany.myapp' is not available. Please enter a different string.
ORIGINAL Answer: The latter part is incorrect - iOS devices use the Bundle Identifier to differentiate between apps. I can have 20 apps labeled "Cool App" on the same iOS device so long as they have unique bundle identifiers such as com.mycompany.coolapp.1 - com.mycompany.coolapp.20. Likewise (and I've done this accidentally) if I open two projects, both of which have bundle identifiers com.mycompany.myapp, and run one right after the other the last app to be run will be installed on the device whereas the previous app will be overwritten.
Regarding the app data sustaining itself I have not tested that though I'd be interested in what happens for you!