Once in a while I see that a file is listed in a commit in Tortose SVN changelog and the "action" column reads "replacing".
What does that mean? How is that different from "modified"?
From the svnbook, replacing is different from modified in the following way.
Item has been replaced in your working copy. This means the file was scheduled
for deletion, and then a new file with the same name was scheduled for addition
in its place.