Shulchan Aruch Chapter 593:
If the blessings and the Shofer blowing hold back each other.
Note: The REMA is in brackets 
1. The (Mussaf) blessings of Rosh Hashanah and The Day of Atonement hold back each other. If you do not know all of them, you should not recite those that you know, but instead should not say anything at all.
2. Similarly, the Shofer blasts hold back each other. That is, if one only knows part of a note, he shouldn’t do that part. However, Tekiah-ShevarimTeruah-Tekiah, Tekiah-Shevarim-Teruah and Tekiah-Teruah-Tekia do not hold back on another. If one knows how to do a single one of them or two of them he should do it. [But the blessings don’t hold back the Shofer blasts and similarly the Shofer blasts don’t hold back the blessings. Whatever of these that you know you should recite. Similarly, the order does not hold back and if you prayed before the Shofer was blown, you are Yotzai.]
An individual who did not pray (the Mussaf service of Rosh Hashanah), his friend can not be Yotzai him (1 Paragraph)
1. If an individual did not blow Shofer, his friend is able to blow for him in order that he should fulfill his obligation. But an individual who did not pray the nine blessings, his friend is unable to cover him. [Some argue and say that if his friend was unable to pray he is able to cover him with his own prayer.]
One who is not an expert in both the Shofer blowing and in the prayers
1. One who is not an expert/knowledgeable in both the Shofer blowing and in the order of the Mussuf prayer and he has a choice of two cities; in one they are experts in blowing the Shofer but not in the Mussuf service and in one they are experts in the Mussuf prayer and not in blowing the Shofer; he should go to the place where they are experts in Shofer blowing even in the situation where you are sure of the Mussuf issue and in doubt of the Shofer issue. [However, if you are able to go to the place where they are praying (Mussuf) and there is time left in the day to hear the Shofer afterwards, you should fulfill both Mitvot since the Shofer may be blown throughout the entire day.]
No title (1 Chapter)
1. After the prayer we blow a long Teruah (תרועה גדולה) without any Tekiah. [There are places where the custom is to return and blow thirty Shofer blasts and afterwards to not blow again at all. But a child, even if he reached חינוך (the training stage) it is permitted to tell him to blow (the long Teruah) and he may blow all day.]
If it is permitted to fast on Rosh Hashanah (3 Paragraphs)
1. We eat, drink and be merry and do not fast on Rosh Hashanah or on Shabbat Shuvah (שׁבת שׁובה). However, you shouldn’t eat without limit in order that you shouldn’t get light headed but you should place the fear of G-d before you.
2. There are places who accepted upon themselves that whoever is accustomed to fast on Rosh Hashanah who changes his custom and does not fast, the change did not accomplish anything. [Concerning one who is not afraid for his life, it is not necessary to fast any (extra) day of his life except if it is required for an abolition (of a vow) like other vows.]
3. One who fasts one time on Rosh Hashanah the fast of a dream, if it was on the first day (of R.H. in exile) he must fast both days his whole life. And if it was on the second day, he must fast his whole life only on the second day. [It is not necessary to give up fasting for there are those who say that it is a Mitzvah to fast on Rosh Hashanah. We don’t say ענינו on Rosh Hashanah just like we don’t say it on Yom Kippur (The Day of Atonement)]
Translated by Jay Dinovitser 7/20/06 www.shulchanarach.com
 The Mishna Brura says that a Chazzan praying in front of ten or more men (a Minian) may cover such a person. The Shulchan Aruch is talking about a case where an individual wants to cover his friend. The reason is that on Rosh Hashanah, every person must ask forgiveness from G-d himself and not through a messenger. But he may do so through a Chazzan with a Minian.
 M.B. Blowing the Shofer is a Biblical commandment and the Mussuf prayer is a Rabbinical commandment. A Biblical commandment outweighs a Rabbinical commandment. Also, a doubtful Biblical commandment is better than a certain Rabbinical commandment. To clarify, “sure of the Mussaf issue and in doubt of the Shofer issue” means that if you are in doubt that that city is knowledgeable in blowing of the Shofer, but certain that the other city is knowledgeable in the order of the Mussuf service.
 M.B. This is to confuse Satan in order that he should not attack us after the prayer when we go eat, drink and be merry by saying that we don’t fear the impending judgement (when Moshiach will come, the Shofer will be blown and Satan will be killed according to tradition). We don’t have the custom to do this, but instead blow a long Tekiah (תקיעה גדולה) as the last Tekiah blast concluding the 100 blasts we blow.
 The Mishna Brura writes that our custom is to blow 100 Shofer blasts: 30 alone/sitting/separate (not in the order of prayer), 30 according to the order of prayer, 30 after prayer plus ten extra.
 The M.B. says this is referring to someone who fasted three times or more times so he has a presumption of fasting. –End M.B.
The individual is unable to change his custom. The M.B. also says that one is only permitted to fast during the day but on Erev Rosh Hashanah everyone forbids fasting and the same is true for any Festival. M.B.: one who does fast on Rosh Hashanah should learn the whole day or spend the whole day in prayer so that his repentance should reach G-d.
 The M.B. says that this applies even if it falls out on the Sabbath.
 The M.B. says that the Halacha is not like this and one who accepted upon himself to fast on like R.H. is like someone who accepted upon himself to fast on Shabbat or Yom Tov which is invalid (since it is forbidden to fast on these days except for rare instances). Except, here the reason why one may fulfill a vow or personal tradition to fast on R.H. is that there are some who say it is a Mitvah. Otherwise, you would not be allowed to do so.