It used to be that the Message Center (display that shows odometer) would display the vehicle is cleaning exhaust, but that was removed a couple flashes ago. Now, the only way to tell is know the difference the engine sounds like, whether it feels like it's surging a little at idle, or by pressing the Setup > Reset button and cycling through the various settings. Toward the end, it will show it's in Regen or not, if no message about Regen is shown, then it's not in Regen.
The flaming issue was addressed around the first or second flash that came out on our vehicles, only appeared on Job 1's if I recall. It's very unlikely any vehicles exist anymore with the flaming exhaust, so you probably won't have to worry about that.
When the vehicle goes into regen, one of the things it does is add extra fuel on the exhaust stroke which helps to burn out the soot in the DPF. When the vehicle is nice and warm, this is usually not a problem as the rings have expanded to make a nice seal on the piston walls, thus preventing the fuel from slipping past the rings. However, when the vehicle cools down, and the rings contract, any excess fuel in the cylinders can go past the rings and end up in the oil. This is typically called washing the cylinders or cylinder wash. If you continue driving and let the regen complete, you reduce the chance of this happening because your giving the vehicle time to burn off this excess fuel and return to normal operating levels.
Other then letting the vehicle complete the regen completely, there are two other ways to cancel the regen, turning off the vehicle or putting it in park. In both cases, the regen is automatically cancelled and will resume at a later time, usually when your about a mile from your destination again. However, since it's only adding fuel during an active regen, what you can do is continue to your destination, pull into your parking spot and put the vehicle in park. Let the vehicle idle for a few minutes so the EGT's can come down to normal levels and this will give the vehicle enough time to burn off the excess fuel that may reside in the cylinders preventing cylinder wash.
If you just put the vehicle in park and just turn it off, you get two negative side effects. The first is that you end up washing the cylinders removing any oil residue which can cause excess wear over time. The second thing it does is cause you to make oil. The excess fuel washes the cylinders and ends up in the oil causing the oil level to rise as well as diluting the oil itself. Again, this can cause excess wear over time as well. again, to prevent either of these from happening, it's best to let the engine finish the regen if your still driving or to place the vehicle in park and let it cool down sufficiently before turning the vehicle off. Some people may argue it's not 100% effective but it's still more effective then just turning it off.