There is a
plugin that is more of a proof-of-concept that would be very convenient to have as a built-in function: be able to use a function in the find/replace. It would allow for a myriad of possibilities only limited by the users ability to create the function. With access to a "Saved Functions" list it would reduce time spent...
For example: making a function to replace text with Title Case
This idea is unabashedly stolen from
Calibre with Kovid's blessing to use.