Hello, Sasq! Thank you for responsiveness!
I made this steps:

"def\vehicle\addon_hookups\glass.MY_MOD"
"def\vehicle\addon_hookup_storage.SOME TEXT OF YOU"

I used "ETS2Studio" to edit *.tobj files.
I've found these lines in "def\vehicle\addon_hookups\glass.MY_MOD" :

1) accessory_hookup_int_data :
2) data[]:
3) physics_toy_data :

Does this lines linked to some files? For example, in your "National scarfs" I've found this:

1) accessory_hookup_int_data : scarf_01.999_toys.addon_hookup
2) data[]: .scarf_dri999.phys_data
3) physics_toy_data : .scarf_dri999.phys_data

But there's no files with such names. Is it random names used only inside this file? Like comments or so?

And another question about *.pmc, *.pmd.
I saw tutorial video but I still don't got it... Do I need to create 3D model of scarf to take *.pim, *.pit files and then convert it to *.pmc, *.pmd? Or another simlier way is exist?

I'm sorry, I'm not good in programming and I never used Blender before, I didn't find intelligible instructions on youtube or somewhere else. :c

SASq, can you make some tutorial how to make new scarfs (with new slots in shop)? I already have designs (*.dds files), but I don't know how to make *.tobj, *.pmc, *pmd files (is it binaries?). I can't find tutorials in google and SCS forum, maybe I was blind. :c I've downloaded Blender and SCS tools, but I don't know how to make this magic T_T.
I want to make new mod and share it to community. Please, help me!