Is the husband's statement to his wife: "Consider yourself in 'iddah from such and such a date, and act accordingly" considered a divorce?

If the husband did not intend divorce by what he said to his wife, then nothing is incumbent upon him. However, if he did intend divorce, then it is effective from the date he specified.

He may reconcile with his wife before her iddah (waiting period) expires if he has not divorced her before, or if he has divorced her once. But if he has divorced her twice before this divorce, then she is forbidden to him, and she will not become lawful for him unless she marries another man willingly, and then he divorces her after consummating the marriage.