I always use the 'Spawn full body morph' option. I'm not real sure what the difference between the two are but I know that Spawn will combine all your active morphs into one single morph. By active, I mean any morph in the figure that has a setting other than 0.0. You won't need any of the morphs you used present in the figure once you spawn the new morph. However, any clothing that uses those morphs will need to be refitted to the new, single morph. That may be as simple as transferring the new morph to the clothing via the figure menu (Copy morphs from) but you may need to make some adjustments in the clothing afterwards.

Zero the figure and then dial the new morph to 1.0. You might also want to match centers to the new morph (right click the morph dial and you'll see the option for that).

From there you can use the export INJ option from the file menu, name it and save to your runtime - usually in the Pose library. It should include the new joint parameters, if any, generated from match centers. You'll need to create your own thumbnail and REM file if you want those included.