I just finished reading the third edition of The Sword Stained With Royal Blood.
There are some major changes here and there.
1) He Tieshou doesn't fall in love anymore with Qingqing. She immediately saw through she was a girl. But Jin Yong turned He Tieshou into martial arts fanatic. When she saw the skills of Yuan Chengzhi, she immediately wanted to become his student and learn his skills.
She couldn't care less about her 5 Poison/Immortal Sect anymore.
2) The martial arts school of the Wen family has changed from Shiliang to Qixian. But they are stil despicable.
3) Yuan Chengzhi is smitten by princess Changping immediately after meeting her. He often would think about her.
4) The Golden Snake Swordsman developed a new martial arts style in memory of his love for Wen Yi. Very romantic of him.
5) The prince who wanted to usurp the throne of emperor Chongzhen is not a fictional character anymore. But Jin Yong used a historic figure, a brother of Chongzhen. Zhu youmo, prince of Wei. Here this usurper didn't die and escaped Beijing was later captured by Qing soldiers and killed I believe.
6) More information on other rebel leaders of that time and on Li Zicheng.
7) Jiao Wan'Er is in love with Yuan Chengzhi, in the second edition it was not clear. But here there are few times when the readers could read her emotions for Yuan Chengzhi.
8) Jin Yong wrote more about the chaotic situation when Li Zicheng was driven away from Beijing. The Ming kings fighting amongst each other etc.
9) In the end Yuan Chengzhi used the new style form of The Golden Snake Swordsman and gained the upperhand on Yuzhen Zhi.
Lots more but these were in my opinion the most important ones.