I am making a new clothing and I'm in the need for 3rd mesh group (I'm using TSRW).
Is it possible to add the 3rd group with it?

You can add new mesh groups with TSRW. I think the actual thing you do is copy one of the existing groups. Then it asks if you want it linked. This means sharing the same materials and everything so if you change the new material the original will change at the same time. Probably best to say no to that, because it's a hassle having to unlink them later.

Thank for the answer. I don't want to sound like a total noob, but how do I copy the existing mesh group? I don't see any option to do this in the mesh tab, so I'm guessing it will have something to do with Project Contents?

I may be wrong, but I think that was a feature in earlier releases of TSRW that they took out. Do you HAVE to have three groups? You can use the mesh tool kit to combine some of those or switch over to CTU.

Yes, I need the 3rd group. I used a top and bottom from EA meshes to combine into one and now I have another mesh group to be made transparent. I'm not sure how Mesh Tool combines stuff, but it crashes with my wso files and I don't want to switch to CTU as I have no idea how morphs and stuff is added with it. It would take me a lot of time to learn everything for it.

You can not copy meshgroups on CASparts but you can add a 3rd meshgroup(atleast in earlier versions) with S3PE and then reclone the file with TSRW.
I even uploaded one or 2 but were......

Instead of searching here you have one.
If you want to try out to add one yourself you can follow this tutorial: http://www.modthesims.info/showthread.php?t=445332
Adding more meshgroups works the same way.

Edit,
Oh crap, i just changed shaders from the 3rd meshgroup to simskin.(was transparant)
Edit, added another one with a 3rd group that supports transparancy(done on the multiplier alphachannel)
Dont mind the meshes, the file contains duplicates

Oh wow thanks Bloom, this is really a life saver.

Is it ok if I use the file you uploaded for my own outfit? If someone else will be using it, it will conflict I suppose?

Also, which group has the transparency enabled?

EDIT: Just saw the other file, don't mind the last question.

You can clone the file with TSRW.(you have to, it is not a WRK file)
The last meshgroup has other shader(CASsimhairsimple)

Im pretty sure that the lowest lod does not support transparancy(EA setting by default) but you hardly see at that distance i guess

Okay, thank you so much!

i made a mistake when loading the correct shader:
http://www.modthesims.info/showthread.php?t=493347