as I said, Body part, Headlight, and many addons, can others player see that? or just be seen by me only ?

Just by you. They see whatever .dds or texture they have. The only thing they will see are skins.

ok man thx for the answer ^ ^

ps. Thx again for (almost?)every post i've made S14 XD

another question

can mod be installed more than one?

I mean if i have 2 files (rear light together with interior)

can i install it ? and will it has effect ?

You'd have to manually compile the textures you want (I.E open the .dds containing the taillight you like and place it in the interior.dds you like)

Just make sure you get the permission from the people who's textures you use before you edit them.