In other words, instead of committing to buy a fixed amount at a market-determined rate, the Bank of Japan will buy a potentially unlimited amount at a pre-determined rate (price). It is true that the package of measures allows a lot of flexibility for the Bank of Japan to determine long-term rates (in addition to short-term base rates), but also raises many questions.
For one thing, the Bank of Japan is now attempting to control both prices and quantities, which is simply not feasible! On the other hand, fixing 10-year rates at 0% may require to buy whatever quantity of bonds necessary to deliver rate stability, which may mean buying more or less than its target pace of ¥ trillion per year.