yes its possible. But Roadrunner wont read them. (Winamp with the flac plugin supports reading/writing flac tags)
There are various flac plugins and source codes for other programs that allow the read/write of flac tags, I downloded a bunch of them with the intent of making a roadrunner plugin that would read flac. But unfortunatly I dont have that type of programming knowledge, nor the time to learn it.
I speak mostly about FLACTagSupport.dll
which is used for Windows Media Player. Sourcecode is available.