It is very easy to toggle between find and replace functionality.

When you perform search and replace in a file, pressing &shortcut:Find; shows the search pane. Pressing &shortcut:Replace; adds field, where you can type the replace string.

While in the Find in Path dialog, you can switch to replace by pressing &shortcut:ReplaceInPath;. Same way, press &shortcut:FindInPath; to hide the Replace with field, and switch to mere search.