You may filter products according to your needs with category, manufacturer and vendor. Prices will be change only for those products, which has been listed.
Prices may be updated according to percentage or amount. You may define if tier prices, attributes combinations should be update as well.
You may define if need rounded decimal value, as well as set fix price. Fixed price set one value for all listed products.
It is recommended to create restore point each time. Restore point create copy of values before changes. If you will made any mistake or type, you may easily restore it to proper point.