Two different types of solder alloy used in process - allowed or not?
Generally speaking, there is no need to match rework solder to the original reflow material. Not only that, it may be difficult to find out exactly what the original material was. A possible exception would be a board that was assembled using a very low-temperature alloy, while the rework uses a much higher-temperature alloy, and the part spacing is so dense that heat from the rework can affect the joints of nearby parts. This is unlikely, but possible, and would affect rework techniques.

But keep in mind that reflow and rework are not one process - they are two separate processes, so your original caution does not apply.