Help for Aimeos

I wrote a new decorator file and put this in
app/vendor\aimeos\aimeos-core\lib\mshoplib\src\MShop\Service\Provider\Decorator\mydecorator.php.
and its working fine .

Butt when i update aimeos it removes my new created decorator file that i have added in aimeos

it also change the aimeos.js file to defaults which is in
app/public\packages\aimeos\shop\themes\aimeos.js

is there some thing wrong that i m doing

Please guide me about this

Don't touch the core files! You have to create an Aimeos extension for your project: https://aimeos.org/extensions#c139
Put your files there, the directory structures are the same besides ./lib/mshoplib/ becomes ./lib/custom/