If I change the theme using the manifest editor :
SetApplicationAttribute(android:theme, "@android:style/Theme.Holo.Light")
I get :
AndroidManifest.xml:20: error: Error: No resource found that matches the given name (at 'theme' with value '@android:style/Theme.Holo.Light').
Same thing if I try and set Holo.Dark (which I believe is the default).
the platform-sdk is backwards compatible, you can always use the latest and it will work all the way back (unless you use a feature from the latest android.jar that doesnt exist on older platforms).
for e.g. themes will just default to the device default theme on android 2.2