I reworked my Opera SlackBuild, now it can be used to make packages for all three Opera flavors: Stable (not yet released), Beta and Developer. I also included an option to build local ffmpeg libraries for the browser to support H.264 video and MP3 audio in HTML5 players. BTW, thanks to ml4711 from LQ for the solution to my problem with dynamic library linking!
README file for details about possible options.
The SlackBuild may be kind of a mess, but I just wanted to cover all flavors and both 32bit and 64bit platforms so I wouldn't have to change the script much in the future. Why did I unify it in the first place? Well, Opera released the Linux version of its browser in Beta (ex. Next) channel, and a SlackBuild for it would be identical to the one for Developer version, so instead of having two (or three, if you consider an upcoming stable version) identical Slackbuilds I decided to go with one.
You can also see the SlackBuild in my git repo.