Right, that was my understanding. 
But Windows Explorer will open to files with long names if their 8dot3 names are used as parameters.
However, that requires that 8dot3 names have been created by the file system: that may not be true on any particular users computer.
I was trying to encourage you to find some method that could become native to Mp3tag. 
Here's my work-around:
It would be more elegant if the quick opening and closing of the command window could be avoided.