According to my experience with Zeiss folders with various Compur shutters they are o.k. to be closed cocked and yes, you can change the speeds whilst cocked with the exception of Compur-Rapid which has a booster spring in its fastest speed i.e. if cocked you can not change from or to "1/500th".
That said I won't leave them cocked for weeks, though.
Here is a link you may find useful: