How to add more parts for making car mod with extra customization

[The Fletcherism]

I need some help because i'm the beginner so i'm straighten myself out how to convert the car to mw for example.I followed nlgrexf & Aj lethal's tutorial video and now!, i know how to use these tools: zmodeler, cartoolkit, vlted and binary. But the problem, i tested myself to add new part for attachment1 example, i saved file then i started the game .I'm customize a car and select an added part so the new part didn't appear, however,it was still the same stock part.
I need some help how to fix with new part appearance.

[Sonic49PH]

Ok so you may try this:
if you are going to add custom parts, that could be
XNAME_KITXX_ATTACHMENTXX or XNAME_STYLEXX_ATTACHMENTXX
you can also try with others like
XNAME_STYLEXX_HEADLIGHTXX
STYLEXX_BASEXX
(XX indicates the number.)

[The Fletcherism]

So i have to add XCARNAME(name)
Where? In zmodeler?

Here the problem