All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
First of all, we hope that there is nothing wrong with saying the Qunoot supplication in Witr on a regular basis, and it cannot be said that this is a mistake.
A group of jurists held that the Qunoot supplication is desirable throughout the whole year.
The Qunoot supplication in Witr is a matter of difference of opinion among the scholars.
Shaykh Ibn Taymiyyah said in Majmoo’ al-Fatawa:
“There are three opinions of the scholars about the Qunoot supplication in Witr: “The first opinion: It is not Mustahab (desirable) in any case because it is not proven from the Prophet that he said the Qunoot supplication in Witr. The second opinion: Rather, it is desirable (Mustahab) throughout the year, as was reported on the authority of Ibn Mas’ood and others. Also, it is reported in the Sunan that the Prophet taught al-Hasan ibn ‘Ali, may Allaah be pleased with both of them, a supplication that he would say in the Qunoot supplication in Witr. The third opinion: The worshipper should say the Qunoot supplication in Witr in the last half of the month of Ramadan just as Abay ibn Ka’b used to do. The reality of the matter is that Qunoot al-Witr is of the kind of supplications that are permissible in prayer: whoever wishes to say it, he may do so, and whoever wishes not to say it, he may also refrain from saying it. Also, a man is given the option to perform the Witr prayer with three, five, or seven Rak’ahs. Besides, if he performs the Witr with three Rak’ahs, he has the option of performing them with one single Tashahhud after the last Rak’ah or that he prays two Rak’ahs and says Salam, and then prays one Rak’ah. Likewise, he has the choice to say the Qunoot supplication if he so wishes, or leave it, if he so wishes.” [End of quote]
As for prolonging the Qunoot supplication, then it is better to limit the Qunoot supplication to what has been mentioned in the Sunnah, but if the Imam adds and supplicates with the supplications that are in the Quran or Sunnah, or adds a word that does not denote a wrong meaning and it does not contain any Islamic prohibition, then there is nothing wrong with it.
Al-Mirdaawi from the Hanbali School of jurisprudence, said in al-Insaaf about the Qunoot supplication:
“One supplicates in Qunoot with what is mentioned in the Quran, Abul-Haarith reported: “…with whatever he wishes’; this is the view chosen by the scholars of the School. Abu Bakr said in at-Tanbeeh: “In supplication, there is nothing temporary; no matter how often he supplicates with it, it is permissible.’ Nonetheless, some scholars of the School restricted themselves to the supplication “O Allah! Guide us among those whom you have guided.” Al-Furoo’ (which is one of the books of the Hanbali School of jurisprudence) reads: ‘Perhaps what is meant is that this is Mustahab even if it is not obligatory.’” [End of quote]
As for your second question, we have pointed out in the icon of entering the question that only one question is accepted at a time, and that if there are more than one question, then only the first question is answered and the rest are ignored.
Allah knows best.