It's normal operation to apply at least two reflow cycles to SMD boards, e.g. all double side SMD populated PCB. Some components are however restricted to one reflow cycle, e.g. some HV electrolytic capacitor series. Problem isn't the quality of previously finished solder joints but the temperature strength of the part.
Selective reflow solder for repair or subsequent placement can be best done with hot air gun, preferably preheating the board.
A problem can be however involved with "long ago" if any moisture sensitive IC packages are placed. The board has to be oven-dried before the chips are heated up to solder temperatures again.