Is it permissible to repeat the poetic verse: "O Lord, we are like him in distress, so have mercy on servants, all of whom are Dhu al-Nun," and to equate ourselves with the Prophet Yunus (peace be upon him)?

There is no harm in repeating this verse, as the poet's intention is to liken himself to Prophet Yunus (peace be upon him) in distress, need, and reliance on Allah. Likening oneself to prophets is permissible if there is a clear point of resemblance.