What is a good paradigm to tell user about the changes they are committing?

So, I am showing a user-project allocation matrix to the user. The user can "Edit" that, and when they do that, the table turns editable, and they can just change cells.

From a datamodel perspective, each column represents a project, and essentially, each changed cell is a change in the userproject table. Before committing the change, I show a confirmation message, saying that:

Changing user X's allocation on project Y from 25% to 20%. Deleting user B from project P2. Adding user C to project P3 at 50%.

User says "OK", and we save all that using Ajax. And we show the confirmation of all changes that went through.

So far so good.

Questions: User can click "Save" and then keep working. Is it acceptable that next time when user clicks "Save", I overwrite the feedback message with the new feedback message? [The old feedback message is gone from the screen.] In other words, is having a "Save and continue working" paradi开发者_运维技巧gm clear enough to users that they understand that it is essentially equivalent to saving, going for coffee, and coming back and opening the grid again?

How about from project log perspective? Each "save" generates a log event, which I fear users may consider duplicate.

You could try and just show a picture of a disk, or icon of a disk after they do some typing, and then it disappears.