Changing the typeface from the official style in a conference paper
In general you are not supposed to make any such changes. Most journals and proceedings have some form of either "instructions for authors" or template, or both, which you are supposed to follow. If you submit something with a different type face, the most likely result is that it will be changed to whatever the journal/equivalent requires.

If you submit to a conference which do not have any specifications on paper formatting, I doubt that anyone will make complaints about your formatting.

The key point I would make is: if there is a set of instructions/template which you are supposed to follow/use, then you should do so. Otherwise trust your instincts and experience of what consitutes good formatting.