I don't think they can actually stop you. How would they?
Just think about all the stuff rock climbers and other daring-dos do.
(Skiing Clouds Rest comes to mind)
If you have the right equipment and right conditions and experience
and noggin on your head ... then most of the year not a problem.
If there is ice accumulation you are taking a risk. Mainly it's falling ice
that is a big issue. And as the day progresses... that risk can
increase drastically. RIGHT NOW... I would be ok going up Mist.
If you look at the picture of us going up with all that ice... well...
it was not that bad at the start... and it just kept getting worse and worse...
and it came to a point where it was MUCH safer to just continue
up than it was go go back down (we were carrying backpacks).
Crampons would have been in order then.
Was it stupid? Probably
Could we have died? Definitely
So... now we are really careful and mindful of it. But I seriously doubt
they could even fine you if you went over a closed trail sign.
As far as I know... ANY hiking you do in the park... you do at your
own risk.
Have fun and be safe