You should have the nifti_tool already, if you have an AFNI
distribution from the last 6-8 months.

You will also want to set the scl_inter variable to zero, and you
can do them both at once as:

nifti_tool -mod_hdr -mod_field scl_slope 0.0 -mod_field scl_inter 0.0 \
-infiles butterfly.nii -prefix newbutterfly.nii

I'm curious, because you seem to be thinking of the short values
as the "real" value of your data, which makes me wonder why
there are scaling factors to start with.

At any rate, the command above should work, and you should
have that program already. If not, you probably need a newer
AFNI distribution anyway. :)

rich