Today, I decided to update my script and search for a way to easily change how I can load vimrc and .vim/ directory. And vim provides a very convenient way to do it using the environment variable.
VIMINIT- for switching vimrc.VIMRUNTIME- for the .vim directory.
You can use it like this:
VIMINIT=/path/to/custom/vimrc vim
and
VIMRUNTIME=/path/to/.vim vim
You can combine them both as well.