Does anyone know how the part categories work in TS4? What I am looking to do as an example is to add Briefs as an underwear option for males, Right now all that exists is Boxer-Briefs. I have figured out that if I hex edit the item category to 5F BA it will show up in the Boxer briefs, but was wondering how to make it into its own category still searchable as underwear.

I have looked at all of a similar style of clothing (Men's Pants) and do not see any logical place to place my new item.
If anyone has compiled a list of all of the categories, that might help, or if someone knows what file sets each category ID, I would be eternally grateful.

Hmm. "Categories" refers to different things in this game. Are you asking how to set flags (used by the filters), or how to make a new thumbnail? Or how to convert female briefs to a male item? Or the categories in the interface buttons (like "Pants", "Shorts" etc as sub-types of "Bottoms")?

Granthes's ColorMagic will let you view and set all the flags for every CAS Part in the game. It will also show you the internal identifier. However, you can't use this to change built-in behavior, such as gender conversions.

To make a new thumbnail, you can use the CAS Cloner from Simlogical.

For gender conversions, you can use CmarNYC's Mesh Cloner.

If you want to add a new interface button, I don't know how to do that... not sure it's been done!

You'll find links for all of these here: http://www.modthesims.info/showthread.php?t=532317

Thanks Srikandi for your quick response. I found the option in Color Magic under the Edit Flags... button on the final page. I had overlooked it.

What I was trying to do was to create some pants that went into the pants category, If I made up my own Category they appeared, but not in any of the preset categories (like Pants, Jeans Shorts and Chinos)

Thanks again for replying so quickly!