Hi, I am a bit confused by the title.
I thought the reason why Tibetan people call it 'mahayana precepts' is to show that the vows belong to sutrayana?
The 8 precept practice in Tibetan Buddhism is expressly motivated by the intention to gain enlightenment for all beings. In the Theravadin observance the intention is to purify and accumulate merit for oneself. The practice is most often written of in a Gelug context and these writings and websites usually call the practice the Eight Mahayana Precepts. However the actual practice is the same.
I don't think my Sakya lama has referred to them as the Eight Mahayana Precepts but just as sojong.
I mean, besides if you can receive it by yourself after the first time, and you got to be vegetarian or not, there's no big difference between mahayana one's and Theravada ones?
I haven't done the practice in a Theravadin context (although I intend to this year) but my understanding is that there is no real difference in the practice itself.
And my Nyingma Khenpo also told me that you have to get it from a monk once.
I believe it can't normally be given by lay people because only those who have the vow can give other people same vow;
In Tibetan Buddhism you take it once from a lama or a monk and then you can take it on your own before a Buddha rupa. So after you have taken the vows once you can take them from a lama or monk again but they are often busy and can't often give them twice a month or more. So afterwards one can take them on their own.
You can actually take the vow from a layperson if they are currently holding the vow. I doubt that that is done nowadays though.
In fact Jamgon Kongtrul addresses these questions in "Ethics".
Nyunyel is more different than that, it's a bit more... kriyatantra I think. And traditionally it takes two days, the second day you can't eat, etc.
Nyung Ney is in fact a kriya tantra practice. But Khenpo Norgay (Palyul) has said that it is a kriya yoga tantra practice with a highest yoga tantra result (i.e. Nyung Ney can actually result in complete enlightenment after death).
Actually my local Sakya lama emphasizes the Eight Mahayana Precept practice and our local nun says that it is because HE Dezhung Rinpoche emphasized it.
However many of the local Palyul students try to fit a Nyung Ney in once a year just before the Palyul retreat in New York. Various Nyingma and some Kagyu groups are increasingly offering Nyung Ney practice.
But I have received a wonderful text written by Khenpo Jigme Phuntsok (I think it's his own terma), which is a Kriyatantra Avalokesrivara sadhana, in the end it says: keep precepts until the next morning.... so actually it's quite like mahayana precepts. And Khenpo told me that I can do it at home since he already gave me LUNG. So it not even requires first time with a monk (of course I still got the teaching from a monk).
_________________Kirt's Tibetan Translation Notes
"Only you can make your mind beautiful."
HH Chetsang Rinpoche