If you need to obtain Lorentz forces using a modified value of B superimposed on that which is calculated by modeled current sources, I think you will need to perform a cross product using element centroidal values with the VCROSS command, and then average the centroidal values at corner nodes. All this will have to be done with APDL. I expect you will have to write F commands to a command file using *CFOPEN, *CFWRITE, and *CFCLOSE, then read the command file into ANSYS after converting to a structural model. Try the attached input file. After the transient electromagnetic run, I read the last results set and added a constant value to the x component of the B field. I did all the cross product calculation with centroidal data (all of it read in with the ETABLE command), and then averaged the centroidal data at nodes. I wrote nodal forces to a command file which was subsequently read into a structural model.