Hello, not sure if anyone knows how, but might as well as ask, seeing how defaults pregnancy clothing has been done before.
I've already made a non default of the clothing and added pregnant meshes to that.
I have created a default replacement using S3OC but don't know how to added the pregnant meshes.
Is there any way for me to combine the meshes?
They're the same clothing, only one is a default and other is not.
Also I don't have Milkshape. So that might be a problem right?

You can try the Mesh Toolkit Package Tools / Add morphs to package function.

Using the same meshes for both is possible but requires changing the links in the CASP to point to the same VPXYs, or changing the links in the VPXYs to point to the same meshes. IMO it's not worth the effort unless you're comfortable doing that.

Thank for replying and giving me an idea. =)
However, I do have problems getting some areas of Mesh Toolkit working though. On certain taps (select a file) it'll won't even open a new window. Not sure if it's because I'm on windows 7?
Anyways, all I really wanted to do is make a default replacement clothing for some latter expansion packs. And seeing how I can't use milkshape, I use TSRW and add pregnancy morphs that way. I don't mind doing it the long way. If it works in the end, it works. (and if I can figure it out) Unless there is an easier way but I think my computer won't let me use Mesh Toolkit to it's full extent.
Thank you for you response. I shall see if I can do what you said. =)

Could you let me know which tabs in Toolkit aren't working for you? It's entirely possible I messed up! And please make sure you're using the latest version. I develop and test Toolkit on Windows 7 so everything should work fine.

I did have the New version. I re-download because Norton took out a file or two . Retested and the only one that is not working for me is Auto Create Morph BEGO under Auto Tools for GEOM.
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As for your suggestion, I did get around to testing it. Though I might of found an easier way. Just copy the CASP Instance from the S3OC default. And use that on the non default CASP. It turn it into a default replacement when I threw it in my override folder. Though further testing to make sure it works correctly.
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Do you know if you make something with TSR workshop, it turns automatically into base game compatibly? I do not want to accidentally make it for base game. If it helps I followed this tutorial on how make clothing preg with TSR.

You're right, just copying the EA CASP TGI will make it a default replacement. As I recall, TSRW does not make clones of EP and SP stuff into base game compatible. It's easy enough to control - make sure the CASP group ID is the same. The first two digits of the group ID determine the required EP/SP, with 00 being base game.

Ah, I was unaware how easy it is make sure it is for the right game, thank you.
Furthermore, thank you for taking time to help me out. Much appreciated.
*Added - was able to make everything work out. I didn't want people stealing if they didn't have seasons. Here's my finished work . Must say again,thanks so much for the help.