Scrum confusion

A team's Definition of Done can really be modified at any time, especially if changing it improves their process or their ability to deliver. A mid-sprint DoD change would therefore make sense.

I do agree with you that a great opportunity to change the DoD is prior to a new sprint starting, perhaps as a result of Sprint Retrospective discussions. However, that doesn't have to be the only opportunity available to change it.

There is no specific rule when DoD can be changed.

1. It is also a good practice to check any possibility of improvement or change required in DoD at the end of sprint Planning meeting due to newly selected SBI.
2. I found it more suitable to change DoD at the end of Retrospective meeting as product and process feedback is with the team.
3. I tried to avoid any change to DoD during the sprint as it could affect all completed items.

During each Sprint Retrospective, the Scrum Team plans ways to increase product quality by adapting the definition of “Done” as appropriate.

http://scrumguides.org/scrum-guide.html#events-retro

> I think that good moment for change it is prior to starting a new Sprint

It isn't a bad one, which is why the Retrospective is commonly used for this purpose. However, the general principle to be teased out is that inspection and adaptation should occur as close as is *reasonably* possible to the time and place of work being performed.

In the case of the DoD, if it is suspected at any point during a Sprint that quality can be improved, then the DoD may be enhanced accordingly. This helps to avoid technical debt, rework, and other waste. A well-executed Retrospective should limit any such waste to the current increment and the Sprint boundary.