I\'m developing an iPad application for a company. Because of confidentiality reasons they do not want to publish the app to the app-store.
The fulfill the enterpri
You definitely don't!
You can distribute the app via
<a href="itms-services://?action=download-manifest&url=http://myDomain.de/path/to/the/MyApp-Version.plist">Download my cool App!</a>
I'm not sure you need the UDID of each device in the enterprise program. This answer seems to imply you don't need to.
You definitely can push a new provisioning profile without re-compiling.
You'll also have to plan on updating the certificates each year, see:
An app will not run if the distribution certificate has expired. Currently, distribution certificates are valid for one year. A few weeks before your certificate expires, request a new distribution certificate from the iOS Dev Center, use it to create new distribution provisioning profiles, and then recompile and distribute the updated apps to your users.
Source: http://developer.apple.com/library/ios/#featuredarticles/FA_Wireless_Enterprise_App_Distribution/Introduction/Introduction.html
With Enterprise distribution program, you can sign your app with In-House distribution certificate which doesn't require UDIDs. That app can be installed on any iOS device and provisioning profile is embedded in the App. For the apps already written and distributed using AdHoc builds you can codesign .app using codesign tool in your mac to sign the app using in-house certificate and convert to ipa.