Because I use parse, so I did a lot cert routines :http://baiduhix.blogspot.co.uk/2015/04/parse-push-notification-cert-issue.html
My bundle identifier is written and embedded in certs, So I can't change bundle. If I do, i need redo all cert routines again.
However, you can see you bundle identifier contains bundle name and bundle name is your project's name. which means if you change your project name, it will change your bundle name. After that you app is a totally new app. and you need redo cert routines. (However I also explains how to do this at end of this post.)
To avoid changing bundle identifier you can do:
go to Targets->info->Bundle Display Name and change it to whatever you want.
Alternatively, to change project name :