Dave Smart has already answered your first question here:
You can unpack the apk file with apps like AndroZip edit the AndroidManifest.xml, repack it and resign it with this parameters:
"cn=My Name, ou=MyOrgUnit, o=MyOrg, c=MyCompany" -keystore my-release-key.keystore -alias alias_name -keyalg RSA
-keysize 2048 -validity 10000 -keypass fred21 -storepass fred21
And for the second question:
DroidScript creates a app which emulate your js code, which is in the app, Android SDK and eclipse only runs the Android code which was programmed by you.
For DroidScript you only need JavaScript or html to write a app, for eclipse or Android SDK you need Android to write a app.