Yes, part of the rebuild of 200 or so standards included a repaint of the interior to the "horrible green and speckled color". Also, unused cabs were removed, and the end areas were opened up by replacing the transverse seats with longitudinal seats. While the cars kept incandescent lights, the lighting was improved (lights were added, and the bulbs were replaced by higher-wattage "soft white" types).
I'm not sure what mechanicals were improved.
The rebuilds came in two flavors, 3 car married sets, with an operators cab at each end and a working conductor's station in the middle car, and 2 car sets, also with a cab at each end, but no working conductor's station. The remaining conductor's stations were deactivated. A typical 8 car train was 3+3+2, with the conductor in the 5th car (or 4th, if the 2 was in the back). A 6 car train was 3+3, with the conductor in car 2 or 5. Also, 3 car trains ran on some shuttle lines and late nights.
Prior to the rebuilds (and the un-rebuilt), the were A cars (single units, active cab at both ends, working conductor's station), B sets (3 cars, active cabs at ends, "private seating" cabs in centers, working conductor's station in middle car) and Bx sets (similar to B but with 4000-series trailer in middle; the trailers had no cabs).
Another feature I remember about the Standards (motors) was that they came in two flavors, with small and large roll signs. The small roll sign models were older, and the signs were obscured from the inside of the train when the doors opened. The large roll signs were located in the upper pane of a window. The 4000 series trailers had large roll signs located slightly differently from the 2000 series large roll sign models (one window further from center). I also recall that the two types of 2000 series cars had different roof ventilators.