Post [Q] Xperia M Screen PPI

Hi Friends,

I had Xperia U previously and I was able to change PPI value using Build Prop Editor. I want to know how to change PPI value of Xperia M's screen because I don't see screen ppi property in build prop file. Is it okay to add new ppi property to build prop and will it be okay to do so? ie will it give more brightness?

Please guide.. Thanks in advance...