Setting number of threads after launch

When I use the Distributed module, I can add/remove the number of processes after launching Julia or within a Jupyter notebook. Is there any similar functionality with Threads, or must the thread count be set at launch?

as far as I know it needs to be set at launch.

Control is to a certain degree available via Base.Threads.@spawn: when running Julia start maximum number of threads you wish to use (julia -t n), but then only use as many tasks as you wish.