I think Hawkes replaces the reference to Iron Threshold Monastery with Water Moon Priory to correct for what he believes to be an error in the original text. In Appendix IV to Volume 4, there is a discussion on the textual ambiguities surrounding whether Jia Qin's activities in Chapter 93 are occurring in Iron Threshold or Water Moon. In this same appendix, there is a remark relating to the events of Chapter 15 ("...Xi-Feng's shady connection is only with Euergesia, the Prioress at Water-moon"). This comment makes me think Hawkes believed that the conversation between Jingxu (Euergesia) and Wang Xi Feng that is alluded to in the introductory couplet is occurring at Water Moon and not Iron Threshold.
Hawkes makes this sort of textual "correction" multiple times in his translation. For example, he swaps references to the maids Cai Yun (Suncloud) and Cai Xia (Sunset) in Chapters 30, 61, and 62 to address what he sees as inconsistencies (see Appendix II in Volume 3 for Hawkes' elaboration on this particular alteration).
I've never read Hawkes' translation but it's interesting to hear about his "correction".
Though it was obvious that Xifeng abused her power in the Water-Moon Priory, from my understanding, Cao deliberately named the chapter title 「王鳳姐弄權鐵檻寺」 thusly to avoid repetition, which is a common rhetorical device called 互文 (is "intertextuality" a good translation?). Moreover, perhaps Cao was suggesting that it doesn't matter the location, Xifeng was cunning, bold and corrupted nonetheless.
I'd say the "correction" was understandable but in a literary sense, it's 點金成鐵手.
Maybe it's noteworthy that in the earlier editions the name of the Prince was different (「話說寶玉舉目見北靜王水溶...」). Why bother changing a name? Was it because 「水溶」 was too similar to 「永瑢」, someone Cao Xueqin knew in real life? You might be interested in reading this article 《北静王的原型》(http://www.guoxue123.com/hongxue/0001/hlwy/044.htm).
“賴藩郡 is an old fashioned formal phrase used to address royalty such as the Prince.”
Here only「藩郡」 refers to the Prince. 「賴藩郡餘恩...」 means "thanks to the blessing of Your Highness" (「犹言“托郡王的福“。赖，凭借。藩郡：屏藩皇室的郡王。祯：吉祥；福」), according to 《紅樓夢大辭典》(1990 edition, page 25).
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"蕶苓香念珠 is a fragrant group of prayer beads. It’s not entirely clear what 蕶苓 actually stands for."
I think Hawkes replaces the reference to Iron Threshold Monastery with Water Moon Priory to correct for what he believes to be an error in the original text. In Appendix IV to Volume 4, there is a discussion on the textual ambiguities surrounding whether Jia Qin's activities in Chapter 93 are occurring in Iron Threshold or Water Moon. In this same appendix, there is a remark relating to the events of Chapter 15 ("...Xi-Feng's shady connection is only with Euergesia, the Prioress at Water-moon"). This comment makes me think Hawkes believed that the conversation between Jingxu (Euergesia) and Wang Xi Feng that is alluded to in the introductory couplet is occurring at Water Moon and not Iron Threshold.
Hawkes makes this sort of textual "correction" multiple times in his translation. For example, he swaps references to the maids Cai Yun (Suncloud) and Cai Xia (Sunset) in Chapters 30, 61, and 62 to address what he sees as inconsistencies (see Appendix II in Volume 3 for Hawkes' elaboration on this particular alteration).
I've never read Hawkes' translation but it's interesting to hear about his "correction".
Though it was obvious that Xifeng abused her power in the Water-Moon Priory, from my understanding, Cao deliberately named the chapter title 「王鳳姐弄權鐵檻寺」 thusly to avoid repetition, which is a common rhetorical device called 互文 (is "intertextuality" a good translation?). Moreover, perhaps Cao was suggesting that it doesn't matter the location, Xifeng was cunning, bold and corrupted nonetheless.
I'd say the "correction" was understandable but in a literary sense, it's 點金成鐵手.
Ahhh that makes a lot of sense. Thanks!
"the young phoenix will sing more clearly than the old."
Here「清」is better to be translated as "clearly and melodically" because it means「清越」(《漢語大辭典》：清越。「候扇舉而清叫，野聞而應媒。」（《射雉賦》）) when describing music.
「話說寶玉舉目見北靜王世榮頭上戴著淨白簪纓銀翅王帽」
Maybe it's noteworthy that in the earlier editions the name of the Prince was different (「話說寶玉舉目見北靜王水溶...」). Why bother changing a name? Was it because 「水溶」 was too similar to 「永瑢」, someone Cao Xueqin knew in real life? You might be interested in reading this article 《北静王的原型》(http://www.guoxue123.com/hongxue/0001/hlwy/044.htm).
“賴藩郡 is an old fashioned formal phrase used to address royalty such as the Prince.”
Here only「藩郡」 refers to the Prince. 「賴藩郡餘恩...」 means "thanks to the blessing of Your Highness" (「犹言“托郡王的福“。赖，凭借。藩郡：屏藩皇室的郡王。祯：吉祥；福」), according to 《紅樓夢大辭典》(1990 edition, page 25).
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"蕶苓香念珠 is a fragrant group of prayer beads. It’s not entirely clear what 蕶苓 actually stands for."
Interestingly, in the Geng-Chen edition what the Prince actually gifted Baoyu was a「鶺鴒香念珠一串」 (https://zh.wikisource.org/wiki/%E8%84%82%E7%A1%AF%E9%BD%8B%E9%87%8D%E8%A9%95%E7%9F%B3%E9%A0%AD%E8%A8%98/%E7%AC%AC%E5%8D%81%E4%BA%94%E5%9B%9E). The bird 鶺鴒 (wagtails) symbolizes brotherly love, especially in times of need (see entry: https://dict.idioms.moe.edu.tw/idiomView.jsp?ID=18637). Is this another foreshadowing? We'll see;)