Can I have actions that, if taken, cannot be taken again in the following N timesteps?
This is not a limitation.  Which actions are valid can depend on the current state of the system.

To enforce your requirement (changing speed at time T means you can't change again until time T+N), you can add additional information to the state: basically, add how long ago was the last change (where if it's more than N steps ago, you don't keep track of how long, just that it was long enough that a change is now allowed).