Yes, since version 4.6.9 it's possible.
- Convert NewYork and SanFrancisco separately, but use
cmd=tj which processes phase 1 and 2 of osm2po's conversion chain only.
- Don't forget to set a meaningful prefix parameter for both, e.g.
prefix=ny for NewYork.
- Use the same
tileSize parameter for everything you are going to merge.
- The steps above result in two directories you can transform into a third one. e.g.:
java -Xmx1g -jar osm2po-core.jar cmd=m prefix=nysf ny sf
cmd=m is the merge command and
sf the source directories (paths). You can even use wildcards here, but I do not recommend it.
Finally proceed with the merged directory and call phase 3 and 4 with
By the way, there is no difference whether the regions intersect or not. You can even merge NewYork-Detailed, SanFrancisco-Detailed and US-Motorways-Only or sth. like that.