Hi,
All HikaShop core files are overwritten during updates.
All overrides (views, css, emails) are kept ; the view overrides are stored in the template folder so they are not impacted by the update and the css/emails overrides are files with specific name which are not replaced by the update.
For the configuration (elements in the database), all is kept.
When we add new columns for some tables, we always follow a naming convention to not be in conflict with potential custom fields.
In every cases, before doing an update ; the best is to perform a little backup of your files and of your database.
Regards,
Jerome - Obsidev.com
HikaMarket & HikaSerial developer / HikaShop core dev team.
Also helping the HikaShop support team when having some time or couldn't sleep.
By the way, do not send me private message, use the "contact us" form instead.