Hi,
you can't override this, and there's no point to..
because the file (probably a self-extracting archive; made by yourself??) can't be executed unless you decrypt it with the password: then avast shield would intercept, if there's anything malicious in it
you can scan the contents if you open the file with Winzip, Winrar ... and supply the password and unpack it, then scanning the resulting files
I guess there are only SOME exe-fils you can't scan ? or all EXEs on your PC ?