In reply to bigrob:
I did this in winter about 15 years ago from the top cable car station, along the ridge and back. It took me all day with axe and crampons and I just missed the last cable car down, forcing me to walk the green route back to Borovets in the dark (with headtorch), which I reached around 9:30pm. I probably didn't get the first car up though, as I was with skiing friends. From memory, grade 1 Scottish, something akin to Striding Edge in winter, but longer. I noticed there also appeared to be another, perhaps easier and definitely shorter way up, which was maybe used as access to the summit weather station. This can be gained from the bottom of the parallel ski runs coming off the ridge. You may be able to get a lift from some sort of vehicle to the start of that, as I remember a 4x4 type of thing rocking up and dropping off.
Skiing down from the summit did not look like an option for me, but I'm not much of a skier anyway, so left them back at the accommodation.
Might try to find some photos later which may provide further details.
Have a great one