public static class LogTargetManager
{
    private static Logger logger = LogManager.GetCurrentClassLogger();

    public static void SetLogTargetBaseDirectory(string targetName, string baseDirectory)
    {
        logger.Debug("SetLogTargetBaseDirectory() - Log Target Name: {0}.", targetName);
        logger.Debug("SetLogTargetBaseDirectory() - (New) Base Directory: {0}.", baseDirectory);

        var logTarget = (FileTarget)LogManager.Configuration.FindTargetByName(targetName);

        if (logTarget != null)
        {
            // Capture the Target's current Filename and Archive Filename
            var currentTargetFilename = Path.GetFileName(logTarget.FileName.ToString().TrimEnd('\''));
            var currentTargetArchiveFilename = Path.GetFileName(logTarget.ArchiveFileName.ToString().TrimEnd('\''));

            // Re-base the Target's Filename and Archive Filename Directory to that supplied in 'baseDirectory'.
            logTarget.FileName = Path.Combine(baseDirectory, currentTargetFilename);
            logTarget.ArchiveFileName = Path.Combine(baseDirectory, currentTargetArchiveFilename);

            logger.Debug("Logger Target '{0}' Filename re-based to: {1}", targetName, logTarget.FileName);
            logger.Debug("Logger Target '{0}' Archive Filename re-based to: {1}", targetName, logTarget.ArchiveFileName);
        }

        // Re-configure the existing logger with the new logging target details
        LogManager.ReconfigExistingLoggers();
    }
}