I'd like a command where I can change the log directory.

alt+o | IRC| Logging --> click the button at the bottom marked "Logs and buffer saves folder"

or directly write to the mirc.ini

/writeini mirc.ini dirs logdir $sdir="Select directory to save logfiles in"

Make sure you know what you're doing tho.

He means change directory on the fly, and by a script, I think

I know, but I stick with my suggestion.

I know what he meant, and since a command is available via script (like I put forth), I remember reading on these forums that there is little chance such things will be implemented.

Didn't debug lack the option to name the debug log file once?

That writeini won't work. If you write to mirc.ini while mIRC is running (which is what is going on, because mIRC must be running to use /writeini), then the changes do not take effect.

I never bothered with writing to the mirc.ini, but I have been told there is a command available to reload the mirc.ini while mirc is running so that changes you manually made will take effect. (/saveini) Or did I misinterpret and is that the other way around?

It's the other way around. /saveini forces mirc to write to mirc.ini (and other .ini files) its own settings (kept in memory until then). There is no way to modify mirc.ini and keep the changes when mirc exits (unless you crash mirc or your OS).