NVDA f is used for formating information and it is so long established that it should be left as it is. That is particularly so since JAWS uses the same command to announce formatting information, and that makes using the two screen-readers more similar and helps in a transition or if people use both.

Why don't you use the search command as it is? I would think you could change it to something else, since NVDA lets you change keystrokes for commands. But you may want to choose something other than what you initially specified since you would then have to change the announce formatting command and the letter f, standing for formatting, used with the NVDA key is a logical command.

Gene