Template customization and bootstrap.

-- HikaShop version -- : 2.6.3
-- Joomla version -- : 3.6.2
-- PHP version -- : 5.6

During template development we met a problem that not all Hikashop files could be overrided in the template html directory. Part of html markup and javascript is mixed with code, besides in the admin files of Joomla.
This applies to files from directory /administrator/components/com_hikashop/helpers/ , for example, cart.php
Also I would like to ask, how we can choose Bootstrap version? Now we can do it only in /administrator/components/com_hikashop/helpers/helper.php:3507 but it will be rewritten after updade. How we can manage it?

Thanks for reply, nicolas.
Can you tell me, please, if the file and class names are correct in that example?:

Original name/address
/administrator/components/com_hikashop/helpers/cart.php
hikashopCartHelper


Override:
/templates/mytemplate/html/com_hikashop/administrator/helpers.cart.override.php
hikashopCartHelperOverride

File with an override is not loading. Is there any mistake?

Thanks for reply, it was useful. Here
www.hikashop.com/support/documentation/6...tation.html#override
is written:
«You can do it by copying the file in administrator/components/com_hikashop/XXXX/yyy.php to templates/YOUR_TEMPLATE/html/com_hikashop/admnistrator/XXXX.yyy.override.php (for the frontend)»

An error was that between XXXX.yyy instead of "." should be slash.

Class methods overriding happens even when it's initialized, and without including to the parent class, just like:

class hikashopImageHelperOverride {

}