To search for a word but not with [ ] squared brackets:
(?<!\[\[)George Bush(?!\]\])
to search for all YYYY-DD-MM in [] and replace it with YYYY-MM#DD
\[\[(\d{4}-\d{2})-(\d{2})\]\]
[[$1#2|$2]]
To search for a external reference and change to obsidian page reference
\[(Marc Andreessen)\]\(https?:\/\/[^\)]+\)
[[$1]]
To search for a external reference and change to obsidian page reference
\[([^\]]+)\]\(https?:\/\/[^\)]+\)
[[$1]]