AFAIK, it is not possible to remove and rebuild an application with a different signing key - the signing key is used by BB to identify the author so removing and re-signing would create problems with rogue apps. But that is only my opinion.
What it is possible to do, is to sign an unsigned application with any key you like.
As a developer, I actually have signing keys that are used by clients so that I sign their apps using their key. So this is one option that you can use, supply the outsourcing company with your keys.
The other option is to get unsigned applications from the developer. These will run on the Simulators, but not on a device. Then you can sign and publish. I am guessing this would be your preferred option.
The problem comes if you already have an application out there that has been signed using your developer's keys. By out there, I mean on BlackBerry World.
Assuming you can get an unsigned version with a higher version number to that on BB World, that you then sign, the implications are:
- For a BB7 and earlier - none, sign and submit it should work OK
- For BB10 and later - you will have to add a new application
If you can only get an unsigned version with the same version number, then the implications are:
- For a BB7 and earlier - lie when you submit your app and give it a higher number
- for BB10 - you will have to submit a new application, so the version
number is not relevant
Assuming you can only get a signed version, then, I think you are out of luck.
Just my opinion...