(Owensville, Missouri, United States)
This question is mostly something i couldn't find a topic of it, because it kinda mixes them. What do crosses do to vampires? And can a vampire's face and eyes' change like on movies (like Buffy the Vampire Slayer)?
Crosses and other religious iconography can be effective in warding off dark spirits, such as vampires, but they only work if the person using them has a strong spiritual connection to higher powers through that symbol.
For example, Catholic priests use crosses when performing exorcisms because to them the cross has a strong spiritual meaning. They use these symbols to personally connect with their higher power (in their case, God). Other religions use other symbols, such as the universally used gemstones which are believed to each intensify a different type of spiritual power. Each physical manifestation of these symbols (such as holding an actual cross made of wood) is what Native American tribes called a "totem". A "totem" can be any object (a rock, a cross, a drawn symbol) that has a strong, specific spiritual meaning to the user. In every case, it's not the symbol itself that is important, but the user's connection to the symbol that matters. If you only believe that a stone of black tourmaline will ward off evil, then a cross will do you no good at all, even if it works for someone else.
The question then becomes - why use a totem at all? It's mostly a psychological tool. Even the most devout of humans is going to have doubts when faced with a dark creature who intends them harm. Having a "charged" totem in hand helps us to feel secure and know that the power we believe in is there with us.
As for changes in the face and eyes of vampires, there is thought to be a certain minor change in eye color and face shape when a vampire is either angry or about to feed. The eyes are said to become more red during this time - settling anywhere between a reddish-brown and a full-on blood-red color. The face does change in the same way a (very) angry human's would - veins bulge, the jaw tightens, and the creases around the eyes and forehead become more pronounced. However, there is no evidence to suggest that these facial transformations are as severe as those seen in movies and television shows, such as Buffy the Vampire Slayer. Chances are those are exaggerated for visual effect.
Then again, I've never come face to face with a vampire who was ready to feed on me, so it's hard to say for sure. I highly doubt anyone who were put in that situation would live to tell about the details.