On the issue of changing the baseline average and control limits - Davis Ballestracci gave me a great quote once - the baseline is innocent until proven guilty. You do not adjust the baseline until there is a significant change or trend in the data. And the signal for a significant change or trend is tripping one of the SPC trend rules, such as 7 points above average. Now, sometimes the data return to the previous baseline after corrective actions are taken, and in that case the baseline would remain the same. But if the data steady out at a new baseline average (or standard deviation), then the baseline would be changed.
Have I posted "The Life Cycle of a Trend" here? I wrote that up with an illustrative example a few years back.