Hoàng ~ Huỳnh 黃
Vũ ~ Võ 武
Chu ~ Châu 周
Hoa ~ Huê 花
Phúc ~ Phước 福
Cảnh ~ Kiếng 景
Hoàng ~ Huỳnh 黃
We've already known that people in Central and Southern Vietnam had to change their surname from Hoàng to Huỳnh because of Nguyễn Hoàng 阮潢 - the first Nguyễn lord in the Central/South
http://en.wikipedia.org/wiki/Nguy%E1%BB%85n_Ho%C3%A0ng
In Vietnamese tradition, birth name of rulers are "kị húy" (something to avoid mentioning). So since the birth name of the first Nguyen lord was Hoàng, people were forbidden to say it. If their family name was Hoàng, they had to twist it to Huỳnh when they said it.
However, the character was still written as 黃 (Hoàng) and not 熒 (Huỳnh) or 螢 (Huỳnh). I guess this was because the character in Nguyễn Hoàng's name was 潢 and not 黃 (Hoàng the surname), so people were allowed to keep it.
As I know, people had to avoid not only speaking the given birth name of the ruler, but also avoid writing it. If a person's name was the same as the ruler's, they had to change it. If they accidentally wrote some words with the ruler's name character in it, they would be beaten.
Today, Hoàng surname is popular in the North but rare in the South, as such Southerners mistakenly think people of Hoàng family have Chinese origin since it's rare among them. Huỳnh is popular in the Central and the South but rare in the North.
Chu ~ Châu 周
Because of Lord Nguyễn Phúc Chu 阮福淍
http://vi.wikipedia.org/wiki/Nguy%E1%BB%85n_Ph%C3%BAc_Chu
Note though, not all Chu and Châu are interchangeable. Chu and châu were originally pronunciations of different characters.
Characters such as 州 (land, continent), 珠 (pearl)...are all read "châu", not chu. We say châu lục, trân châu...no one says chu lục, or trân chu
Hoa ~ Huê 花
Because of Hồ Thị Hoa - the Queen of Minh Mạng
http://vi.wikipedia.org/wiki/Minh_M%E1%BA%A1ng
Phúc ~ Phước 福
Because almost all Nguyễn lords/kings got Phúc as their middle name
Cảnh ~ Kiếng 景
Because of Prince Cảnh
http://vi.wikipedia.org/wiki/Ho%C3%A0ng_t%...AD_C%E1%BA%A3nh
My question is...If rulers' birth names were all kị húy, how come we still keep so many pronunciations like lợi (profit, benefit ~ Lê Lợi), tráng (Trịnh Tráng), kiểm (Trịnh Kiểm), kim (Nguyễn Kim), ánh (Nguyễn Ánh)
My guess is that when the ruler died, people reverted back to the old pronunciations. Like flower today is Hoa, not Huê (I rarely see anyone say Huê). Landscape today is phong cảnh, not phong kiểng.
But in a few cases, the changes stayed for so long that it became permanent in the language of Central and Southern Vietnamese. Especially when it's something that involves a family name, the changes are more likely to become permanent.
