Thank you for the info
But while dealing with some other issues I realized that I had a possible solution to this problem. It seems that all I have to do is to use the FreeCommander as a filehandler and set in it a hotkey for a shortcut in Tools > Favorite tools > Favorite tools edit [which is an equivalent to shortcuts from File > Options > Tools in Mp3tag]
And if that hotkey is for example "CTRL + 1", then the "CTRL is pushed" and the files are not send to Mp3tag but are added to it; and the window of Mp3tag is put in front. And that is even quicker than having to evoke the shell menu and search in it for the MP3tag shortcut