Is it possible to re-roast a previously roasted coffee? Maybe yes, if the following conditions are met!
The previously roasted coffee color is uniform. If not, then the darker color might get burnt or the lighter color might not get enough heat. The non-uniform roast will result to a non-uniform end.
In case the previously roasted beans was not uniform, the roaster or any other personnel is willing to sort it to two or more groups. The re-roasting time of each group will depend on current color and the desired end.
A veteran roaster. If the err roasted coffee beans were roasted by a newbie. Then an expert might do something to correct it.
The roast color should not be beyond the desired. Converting a dark roast to medium roast is ridiculously impossible.
The roasting machine should have a see through glass window for monitoring bean color. It allows immediate stop and eject when the desired color is achieved.
Re-roasting coffee is not recommended. It is a deviation from standard protocol which might render significant flavor difference.
The picture below was an example of re-roasted coffee. An attempt to convert light roast to dark roast. It went well with a slight perceptible deviation in overall flavor.