Meska: to hide clothing or hair, the 'flags' entry in the Property Set needs to be increased with 1. If the current value is 0x00000000 turn it into 0x00000001, if it is 0x00000008 make it 0x00000009 and 0x0000000A becomes 0x0000000B.

Default clothes and hairstyles are listed in <game or xp>\TS data\Res\Catalog\Skins\Skins.package

To unhide, decrease the value with one.

If you open these mods in SimPE you'll see that they only contain the property sets for the clothes, I used a hex editor to find/replace the flags values.