Swithing PAL/NTSC mode from the OS in Raspberry Pi, possible?

In Raspbian, we have this “tvservice” command that allows to change the physical video mode from within the OS.
In RISC OS, I’ve not seen a way to do this after the system has booted. Of course one can specify the SDTV mode in config.txt, but I’d like to do it from within the OS like it’s done with tvservice on Raspbian. Is that possible?

I think that is the (only?) thing missing that prevents RC14 becoming a stable release. Messaging between RISC OS and the GPU (to find out what resolution the GPU is sending to the monitor for example) is not yet working AIUI.