Will trying to flash an unofficial update with stock recovery harm my device? I have an Android tablet, the DigiLand DL718M, with a stock recovery that can do slightly more than expected. It isn't much, but I have high hopes that it will support flashing SuperSu using the recovery. My question is, if I try to flash it to test it out and it turns out that my stock recovery cannot install custom updates, will it damage my firmware or something like that, or just pop up an error message telling me I'm an idiot?

PS: I'm explicitly asking about the stock recovery for a good reason: This device's bootloader is not unlockable, so I cannot install a custom recovery.
Stock recovery should just fail, it will look for a digitally signed package from the manufacturer, not find it, and error out without making changes. If the developer who made the package specifically made it to work for that device and spoofed the signature somehow, it could do anything from work perfectly to perma-brick the device, hard to say.