Maybe I didn't check the rules well, but can someone tell me if a Level 2 General, who enters a Fortress Area besieged by a friendly Level 1 General, can subordinate to the besieging General? If yes, is the Siege still on or should be lifted?
It continues since subordinating is not a forbidden action; see this play note
"Play Note: Subordinates and Siege Markers: A Siege Marker is always placed on the Army on the map. Subordinates are free to come and go without disturbing the marker. However, if another Army wants to Subordinate the Sieging Army, the marker will be removed (and will cost a Movement Point—if the MP cannot be paid, the movement cannot be completed). This is because the siege lines are set up by the original Army, and the coordination of Armies was insufficient to permit simply switching who mans the lines. 17th Century English armies were triumphs of extemporization, not of experience."