Normally just changing the package version and checking for the source url (if it is not using the $VERSION parameter) and things should work ok.
The problem with some packages is that some developers don't maintain de consistency of its packages, so opera, for instance, seems that every single version the url changes completly and the installer script changes as well.
As of transmission I don't think there should be a problem.
I just think that since the new version of transmission (2.xx) now have a qt4 and gtk gui interfaces, maybe you will need too force the use of gtk with --enable-gtk flag on the configure command, but nothing else.
If you need help creating specs for some packages you can take a look at how the other distributions like archlinux and gentoo, and use the site that kim88 have created a long time ago that provides a step by step to create a spec: http://upkg.kim88.ch/
If you have a problem with your transmission spec, please create a thread here requesting the upgrade and posting the upkg and the error you're receiving that I'll try to help you futher, (just as an advise so we don't get poluted threads, please create an independent thread for transmission and let this place be only for opera package discussion)
* Just to remember, I'm not a developer and so I can't upgrade or fix the packages on the repository (as one once asked me to :/ ), but as part of the community I'll try to help where I can, answering these threads.
** zerobug, try the version and if it fails, you will not lose the installed package (only get a compilation failure). And so, if the failure appears, you could come back to the forums and ask for help (posting the outputs).
OSs: Paldo-testing x86_64 :: HP Pavilion dv9680ez