depends on the shutter -- never heard of large format shutters you couldn't change after they are cocked, not sure why they should be different than those on a scale focus compact 35 or anything else. Both copal and Compur made shutters that work with cams that adjust the degree of delay by adjusting the throw on a retarding gear train.
The ONLY exception to the "go ahead and change it after you cocked it" rule is the older compur shutters that have a second spring that is engaged when you shift to the top speed - ie. 1/500th, mostly found on older Rolleis and Zeiss, such as my Ikonta Super B andC -- on these you have to engage the top speed BEFORE you cock the shutter and fire it before you change it back to a lower speed. You can easily spot these shutters because shifting it from 1/250 to 1/500 you can feel the definite added amount of force it takes.
By the way, even shutters for large format cameras don't have different springs for different speeds, except for the shutters that have the extra for the top speed. The Kodak Supermatics don't use it, for example, and I have one of those on my speed graphic.
With or without the extra spring, just as an aside, the top labeled speed is rarely achieved as marked, especially on older shutters that haven't been serviced in the last 30 years or so. Pretty amazing they work so well, but that's how they used to make things.