Can we simply rename an app if they are different versions and keep them both?
There are several things to look at here:


Application (folder)


It's usually perfectly save to rename the application (aka the application folder) so you can easily rename the existing Xcode to /Applications/Xcode 4.4.1 and install the new version in parallel


Preferences


Typically the application saves it's preferences in a fixed location in ~/Library. So if you have two versions installed in parallel they will both read and write from the same preferences files. This may be desirable from a user point of view but will lead to problems if the format or content changed in incompatible ways.


Addons


As far as Xcode is concerned, there is additonal software installed (automatically and/or on user request) in /Applications/Xcode Utilities. If you need this, it might not be enough to simply rename this folder because you will end up with two versions of these utilities (with Xcode/OS X picking up the "wrong" version)