the advantage of 2 is that you can do an analysis in PT (swapping the cell) that is very close to the post ECO situation since you aren't going to touch the routing anymore.
But considering changing the VT of the cells give a thought on the leakage aspect as well...LVT has more leakage..may affect your design..If you have routing space I would recommend #1 for you.
The physical changes of #2 is only change the cells. No wires will be changed. So, no extra iteration between STA and PR will be required.
BTW, make sure use LVT will not introduce extra layers to your chip.