Half of that bias will always be factored into the computed reduction from the slope distance measured by the instrument to the horizontal distance and the vertical difference. In most cases the bias applied to horizontal reductions will be slight if you work in fairly flat terrain. In computing the vertical difference for trig leveling, this bias is a more important factor and needs to be taken into account depending on your needed accuracy. Follow the instruction manual of your instrument to make the necessary adjustment to your vertical bias. Sometimes this can be done automatically by the instrument or by small internal adjustments.
Regular checks are advisable in any event.
You can combine your leveling with a traverse run without any extra effort, just by extra note keeping. To reduce your notes, begin with a diagram of each setup. Draw a profile view, showing the relationship of the rod above or below the HI, keeping in mind the minus and plus values of the D V. Begin with the known elevation, add the ROD, add a minus D V and subtract a plus D V from the backsight point. Now you have the elevation of the telescope. Subtract the HI to set the ground elevation of the point of occupation.