Use a yum and localinstall like this.
yum --nogpgcheck localinstall packagename.rpm
yum will look and see if you are going to try and overwrite something other then a config file. If you are, it will give you a conflict error.
It is possible to crash a system with foreign rpms, though in this case exceptionally unlikely. If that happens, reboot the system and run.
yum remove packagename
Generally if there is a problem with a foreign rpm, it either will not install, or the application will crash as soon as launched. It is really very rare for an application crash to take the whole system down.
The exception to this is with a foreign package that "updates" an existing system package. That can bork a lot of things. Adding applications though, is usually pretty safe.