How to propose a change in a prayer?
Such a proposal would have to have a considerable following to even to be considered a valid (optional) from of the Hail Mary from the traditional form at the local level. Rome would not be against such a usage as a local tradition.. Praying the Hail Mary in the form you suggest, apart from not being traditional, does not seem inappropriate or pose any problems. It is simply not the form the Church uses in English speaking countries at the moment.
In fact the last part of the Hail Mary was added to the original Hail Mary during the Black Plague.
The “Hail Mary” prayer that Christians have been praying for centuries is composed of two main parts. The first part of the prayer is derived from the Annunciation, when the angel Gabriel greeted Mary by saying, “Hail, full of grace, the Lord is with you!” (Luke 1:28) The next part of the prayer is taken from the Visitation, when Elizabeth greeted Mary with the words, “Blessed are you among women, and blessed is the fruit of your womb!” (Luke 1:42)
At first the prayer was known as the “Salutation of the Blessed Virgin,” and only consisted of the two verses joined together. However, during the Black Plague (also known as the “Black Death”) the prayer was further developed and a second part was added to it.
This second part (“Holy Mary, Mother of God, pray for us sinners now, and at the hour of our death”) is believed by many to have been added during the plague to ask for the Blessed Mother’s protection from the fatal disease.
Venerable Fulton J. Sheen explains this origin in his book The World’s First Love.
Since it seizes upon the two decisive moments of life: “now” and “at the hour of our death,” it suggests the spontaneous outcry of people in a great calamity. The Black Death, which ravaged all Europe and wiped out one-third of its population, prompted the faithful to cry out to the Mother of Our Lord to protect them at a time when the present moment and death were almost one.
How the Black Plague changed the “Hail Mary” prayer
Another example comes from the French form of the Hail Mary contains a few items of interest for us here.
First of all Hail Mary does not conclude with the word Amen, although some French do. While I was living in France, we all said Ainsi soit-il in lieu of Amen.
Second point which I truly love about the French Hail Mary is that they add the words poor sinners (pauvres pêcheurs) to their Ave Maria.
For those who wanted prayers: here's the "Hail Mary.
Je vous salue, Marie, pleine de grâce. Le Seigneur est avec vous. Vous êtes bénie entre toutes les femmes, et Jésus, le fruit de vos entrailles, est béni. Sainte Marie, mère de Dieu, priez pour nous pauvres pêcheurs, maintenant et à l'heure de notre mort. Ainsi soit-il. - Hail Mary Prayer