can I change speeds "on the fly" with absolute tar

[roman]

Is it possible to change "pulse divisor" on the fly when using the ROR or MVP command?

[Andrew]

Yes, you can adjust pulse_div on-the-fly. Speed would change immediately.
However you might want to investigate any issue with positioning posibly resulting from that, as described here:
http://www.trinamic.com/ttdg/viewtopic.php?t=562
I have not had the time to investigate if there's really any bug. I suggest you do it, and report back here.