While I do believe it is technically "off limits", I have climbed there without any problems.
I would suggest a weekday, and I would stay off the face above the tunnel.
I have fond memories of being a little kid driving through that tunnel with my grandmother when there were climbers top roping from above. She freaked out thinking that they were trying to attempt suicide.
Anyway, if you park where the old rest. is and hike up the road for just a short while, you can bushwhack left up to the right end of the crag where there are a few easy routes. The stuff on the main face is wayyyy chossy and dangerous.
Not really worth going if you think you might get caught or you are looking for a solid day out and don't live nearby.
The hiking is great though and it is a little bit of history.
Watch the falcon nesting as well.
Cheers,
Christian :?)