I know that there is possibility to reload any other ini files than mirc.ini. But is there any possibility to do that, without restarting a mirc?
That, what I want to do, is to change one value in mirc.ini using script, but when I change that value, I need to tell mirc.exe to reaload all settings from ini file.
What can you suggest?

I suggest you suggest it, although I'm sure it has been at some point(s) in time. I'd support it.

most of the settings in the mirc.ini file can be changed remotely anyway, without having to edit the ini file... what are you trying to change?