For The Darker Roast
Traditional dark roast is pretty easy. Load the roaster and apply heat. For a traditional oily French I am only going to be roasting for 10 or 11 minutes. You can apply quite a bit of heat early on but be aware that the dark end color is going to mask damage you have done in the early stages of the roast. If you see the beans go through an orange phase, you have burned them early. Be gentle during the drying phase, try keep it to at least 5 minutes, then put the power to it once they begin to yellow. The convection heat available in the cascabel can damage the beans early on. They will turn orange and have a dull rough appearance when they are roasted. You may not notice this once they are very dark but it will affect the flavor so be careful and monitor the process closely. I often dump a few beans every minute or so, or at certain temperature intervals so I can go back and look at them to see damage.
Development is still important with darker roasts, but the char flavor is overpowering so nuances in the bean will be lost regardless of development efforts. You may use crack or after crack as determining factor as to when to begin development. The hotter the roaster and beans the longer it will take to begin development as there is lots of heat to dissipate, so it will take experimentation to get the timing just right. Monitor the beans carefully as they darken as they can go from robust to charcoal very quickly at high heat.
A more modern approach to the darker flavors without such a dark, hot endpoint is to use the hot pan to develop a small amount of char on the exterior of the beans without pushing the end temp super high. The way to do this is to follow the directions for a modern, lighter roast, but do not agitate the beans as aggressively as you approach the development period. This allows for more contact time with the hot metal which will add a distinct charred or roasty flavor, while still allowing the more subtle flavors to come through. This is done by commercial roasters as well, by slowing the drum speed and often lowering the airflow for a while. I see many espresso blends done this way.
Bottom line here is that the roaster will give you whatever results you want, but you will need to learn the process. This is analog, not digital. Manual not Automatic. No power steering or autopilot here. Take notes, save beans and match them up with profiles. Soon it will all become second nature and you will know just from the smell what is happening and how to react.
This is one of the skills that makes a roaster a Roastmaster.
Remember to read the Entire Process of Roasting blogpost!