Well, there are the ActionUndone and ActionRedone events, so you could set it to true from their handlers It's not a problem to clear the Dirty flag from your custom function.

Stoyan

Another question, I use composite commands on large block of code, but sometimes nothing is done in these blocks due to some restrictions and the created composite command is empty.
How to handle empty composite commands, so they will not occupy space in undo history? I guessed, that empty composite commands are omitted in history when calling execute, but that's not true. Also manually deleting items from undo history is not possible. I've also tried merging undo commands, but if there's only one empty command using merge is not possible.

ActionRecording works, thanks.

But another issue is here:
if I start the composite command and then I modify one tableNode in this way

node.DeleteRow(pos);
node.InsertRow(row);
node[0, row].Image = someimage;
node[0, row].ImageAlign = ImageAlign.Center;
node[1, row].Text = somestring;
node[1, row].Tag = sometag;
node[1, row].ToolTip = somestring; 

Then calling undo causes, that the node loses it's treelike hierarchy - it became flat ???.
And then, if I call Redo, the created row is recreated, but it's empty.
Maybe some actions are not recorded into Undo, but is there an easy way, how to fix it?