Many if not all wikis offer a search function where you can search for text across the wiki content, but not a search-and-replace function.

Particularly in cases of wiki pages changing their names, it is useful to be able to change the text of the wikilink throughout the wiki. I believe some wikis offer this automatically when one changes a page name, but I'm not sure. In any case, a global search and replace tool would be useful for other editing purposes besides changes of page name.

This should be no problem for wikis based on text files, as search and replace is very easy with basic unix tools. I don't know how this might work in wikis with relational database content.

One obvious issue is with cross-domain wikis. This would need to be done only with the appropriate permissions. If the linked wiki domain did not give permission, this would need to be flagged as a potential search and replace for people with the appropriate domain permissions.

Unknown.