I have not tried it myself but you can make an attempt with the following, use the code from my post and add valid_elements : "i/em"

That would not be enough. it would alow the i tag to be in the editor but would not change the behaviour of the italic button. it would still create em:s. I would create a new plugin (using the same visual class and such) that wraps curent selected content in an i tag. this should be a pretty simple plugin to make and would be a good practise plugin also. 

Editing the current plugin directly to instead make i tags is not recommended. since i think its a part of the advanced template somewhere or so in tinymce, its not a good place to change things considering future updates to tinyMCE/episerver. 

If you look at the specification for tiny mce it says "/ Separates element synonymous. The first element is the one that will be output. " and I can verify that it works just like that so by using the code above you will get i instead of em.

Ahh great then =) 

Thanks for the info I didnt know that.

Thanks!

You are welcome!