Slitherine

Is it possible to play them stand alone? Like scenarios from other campaigns which you can play after unlocking them.

nope

If you copy the scenarios from:
<game install folder>\Order of Battle - Pacific_Data\Content\Campaigns\3SinoJapWar\Scenarios

to:
<my documents\Order of Battle - Pacific\Scenarios

you should be able to play access them through the scenario screen. I'm not sure if we set up starting resource bonuses in these to compensate from the missing core units however.

If you don't have enough RPs to purchase the missing core units:
Hit Shift + c.
This opens the console window.
Enter #warbonds
This cheat gives you 500 RPs.

Yeah that did it, thanks a lot.