That can only be applied to all models, not just specific ones.  To remove the translations/rotations of a specific model, one possibility would be to create a matrix file with all zeros and then apply it to that model with the command "matrixset".  The command and the matrix format, which is pretty simple, are described here:
<http://www.cgl.ucsf.edu/chimera/docs/UsersGuide/midas/matrixset.html>