Yes, certainly. All you have to do is install whatever version of gcc that you want, and then replace the first gcc on your path with a small shell script that notices when it is invoked with --version and responds with a lie instead of the actual version.
Will it function properly? Who knows ?! Probably not. In particular, I suspect C++ exception handling will not work with code compiled with 6.3 .
But, of course, whether it will work or do anything useful was not your question: you just want to know if it can be installed.
