(There's no video for BNDL Banger yet. Please contribute to MR and add a video now!)
BNDL Banger, as the name implies, bangs BNDL resources. Simply put, it provides an easier way to update an application's BNDL information in a volume's desktop database. Just drag & drop the desired application onto BNDL Banger's icon and that application's BNDL information will be slammed into the desktop database of the volume on which the selected application exists. The next time you reboot, that new BNDL information will be used instead of whatever old BNDL information it had (along with whatever new icons you defined for your application, its documents, its editions, etc.).
This is generally much more convenient, and far less error prone, than rebuilding the volume's desktop (especially considering that rebuilding the desktop doesn't always produce the desired results - see below for more details).
You can also select the application whose BNDL you want to "bang" via the "Banger" menu (there's only one item in that menu, so it's real easy to find the right item). If you go this route, you'll be presented with the standard open file dialog that only shows applications, folders, and volumes. Navigate to the application whose BNDL you want to bang and click on the "Open" button. If the application's BNDL is successfully "banged", you'll be presented with a dialog confirming the action and reminded that you'll need to reboot in order to see the results (sorry, no clean way to avoid the reboot, best I can do is let you avoid rebuilding the desktop).
BNDL-Banger-v-1-3.sit (17.53 KiB / 17.96 KB)
BNDL Banger v1.3 (1992) / compressed w/ Stuffit
Mac OS 6.x - Mac OS 9.2.2
Emulating this? It should run fine under: Basilisk II