Alternative index (with an alternative theme)

Alternative index (with an alternative theme)

I am new both to web-development/php and to wordpress. I've done a custom
wordpress theme and it's ok. I'm using MAMP as local apache/mysql server.
It works with permalinks "post name" setting and I like it very much, but
it is hiding me the real page names.
Now, I'd like to have an alternative index, a page like:
localhost:8888/mywordpress/index2.php
or
localhost:8888/mywordpress/index.php?somearguments
(I don't know which one is the easiest solution)
where I have the same as localhost:8888/mywordpress/ (I guess it's
localhost:8888/mywordpress/index.php) but with some html element more
(like two or three div more, and some js script more). Let's say that it
could easily be an alternative theme.
So, for recap, 2 alternative index:
localhost:8888/mywordpress/ with my custom theme
localhost:8888/mywordpress/index2.php with my custom theme PLUS some more
element
I've tried to read the code of index.php and template-loader.php but the
only clear thing is that I don't have to touch those files (or other
wordpress configuration files).
I tried to google a little bit and I've found some black magic (that I
really don't know anything about) with .htaccess that I am scared about.
I'm looking for the more easy solution (also a dirty one) that doesn't
make me touch some strange configuration that I can't handle.
What is my best bet?