Hi mate,
You can't do it from the Timeline any more.
I believe they locked it because too many people would accidentally click and drag without even noticing and this could have disastrous consequences.
It's happened to me multiple times over the years, but once was really bad as I had moved only a little from 25 to 27 fps.
When it's something drastic you notice right away, but this was at the beginning of work on a project before importing the sounds, so they were mapped incorrectly.
I had animated nearly two minutes to dialog and sound and only when I finished noticed the problem. Had to resync and re-do the work, which was really a terrible thing to do.
I'm curious. Why would you want to change the frame rate frequently?