it looks like the Section 6-25 of the FAQ hasn't been updated in a while since it still talks about the 16 and 32 bit version of mIRC. And running multiple copies of the same.

The instructions appear not to work. I created a new shortcut to the mirc.exe file in Program Files(x86) and created a new mirc.ini file in users\myuser\appdata\roaming\mirc

However, I get an invalid file/path anytime I try to update the Target filed or Start in fields of the properties of the new shortcut. To have it point to that ini location.