Merge for the individual groups is the wrong verb. It is combine. As far as poking thru goes, it does not matter if you conform in Poser, or do a combined figure. The mesh geometry is fixed. The only way to alter it is by morphing. Either externaly applied, or thru the action of joint parameters. If your characters are to be kept clothed, and the clothing has no transparency, then the easiest way is to make the body group underneath invisible if it is fully covered. The most efficient way for file size would be to replace the body part with the clothing part, and combine the half and half parts. If you have a modeling program, you could make a single group from the half and half groups by deleting the covered skin portion and then renaming the result as a new group with the old name.