There is a widespread custom, discussed in a few places on Mi Yodeya (such as here), to keep the last part of a masekhta unread in advance of the siyum. So, for example, if a person has just learnt Pesachim, they might wish to leave the final part of the final sugya unrevised, then learn it in the company of those who are joining them for the seudah. So far as I understand it, this is a custom only, and does not preclude reciting the hadran or the kaddish, and certainly not eating the meal.
My question concerns those who wish to observe this custom, but who are making a siyum in the morning, having just finished either Berakhot, Nazir, Yevamot or Kareitot. All four of those masekhtas conclude with the same brief sugya, which is also included at the conclusion of the davening:
אמר רבי אלעזר אמר רבי חנינא תלמידי חכמים מרבים שלום בעולם שנאמר וכל בניך למודי ה׳ ורב שלום בניך אל תקרי בניך אלא בוניך שלום רב לאוהבי תורתך ואין למו מכשול יהי שלום בחילך שלוה בארמנותיך למען אחי ורעי אדברה נא שלום בך למען בית ה׳ אלהינו אבקשה טוב לך ה׳ עוז לעמו יתן ה׳ יברך את עמו בשלום
Granted, this is only a custom, and granted that there is nothing problematic about omitting this part from one's davening anyway. My question is really about whether one might recite it in their davening and still be observing the minhag of keeping the last part of the masekhta unrevised. Is davening sufficiently distinct from learning as to permit this possibility? Or should one who wishes to observe this minhag be careful not to recite this section in any of their tefillot between completing the masekhta and having the siyum?