Hi,
We try to make new code backward compatible, at least as long as new features are not activated.
So normally, you don't have to redo your overrides.
But it's hard to know whether you'll have to redo them or not.
It depends on what we change, how your shop is setup and how you do your overrides.
Also, you need to be careful of the version number when you update. When it's a minor update (from 4.6.0 to 4.6.1 it means we changed less critical things). When it's a major update (from 4.6.1 to 5.0.0 for example, it means we changed core functions of HikaShop and you might need to adapt more things).
Now, there is a way to minimize issues with view overrides (and that's not only for HikaShop but for any extension, including Joomla's views themselves). When you do the override, instead of keeping the whole code and modifying it, it's better to require the original file and modify variables before, or change the HTML after.
Here is an example for product / option :
<?php
// at the beginning you can change data in the attributes of $this so that it will affect the rendering in the original view file
ob_start(); // start a new buffer
require_once(HIKASHOP_ROOT.'components/com_hikashop/views/product/tmpl/option.php'); // load the original view file
$html = ob_get_clean(); // get the HTML generated and store it in $html
$html = str_replace('', '', $html); // you can use str_replace or preg_replace to replace things in the HTML
echo $html; // display the HTML of the view
Doing it like that, your override will automatically get the code modifications of the original view file when you update. So there is a lot less chance that something would break.
However, it means less freedom in what you can change in the view file. But for small changes like adding classes, or extra text, etc you should be able to do it like that.
Also, don't forget that you can also use translation overrides (to change text) and hidden options or even trigger events to change / add things to views without creating a view override.
To me, the view override of the whole code of the view is really the last resort when I can't do what I want any other way in order to minimize the troubles for future me.