[DiapDealer]

No. RepoLog has nothing to do with debug logging. On Windows, create an environment variable named SIGIL_DEBUG_LOGFILE and set it to a path (including the file name itself) where you want debug output to be printed. Then use Qt's qDebug() function to output stuff. There's plenty of examples in Sigil's code. Microsoft makes it nearly impossible to get any console logging happening from a Qt gui application. But I hear some people have luck getting a cygwin/bash prompt to show the stdout/stderr of a running program.

The answer to your previous question is "it depends." If you've changed nothing in any of Sigil's libraries and support files then you might be able to get by with replacing just the Sigil binary. I play it safe, myself. I find the time it takes to install sigil is trivial compared to the painfulness of configuring/compiling Sigil on Windows.