1.) This doesn't require a mass action. There is a setting for the default "Quantity input method" in the configuration. For some reason the documentation doesn't show it, but you'll find it under -> System -> Configuration -> tab Display -> Default parameters for products.
This is then true if you didn't override this default setting elsewhere, e.g. in product edition pages, but leave it at "inherit".
2.) The way that HikaShop have set up mass actions and its interface, you don't need to be a programmer to perform them. And you can't mess up things if you use common sense, and - most importantly - always create a backup before any major change, including the database!
All on mass actions see here:
www.hikashop.com/support/support/documen...massaction-form.html
However, if you feel uncomfortable doing it this way, you can also export your products, perform the changes/updates in a spreadsheet app (e.g. Excel or Open Office), then re-import. Again, the documentation helps you with export/import, and so do many, many forum posts here... there are even dedicated forums for both mass actions and import/export.
3.) HikaShop 2.5.0 is out since a while, it's just not been included with the auto-update. But you can download it here via -> My account -> My subscriptions, and install it over your current version.
