The above should work how you asked - however, there are some ways to make it a little more slick if you would like - but there seem to be a few more unexpected behaviors from Opus in those ideas as well...
For instance, you could remove whatever default actions exist for the individual filetypes (say, CB7, CBR, and CBZ files)...
You could then create a redirect using a new Opus File Type Group, to which you would assign the 3 file extensions as members of the group, and then assign a Left double-click action that runs something like:
go newtab
[
show slideshow
]
This would let you not mess with internal viewer and other settings and instead tell Opus that for those file extensions, open the archive (the go newtab command), and then uses the 'embedded commands' feature to run a subsequent command once the archive is opened (the show slideshow command inside the square brackets).
But a few issues here... once again, this runs into a limitation that perhaps GPSoft could tweak. You might notice that I'm running a go newtab command. This opens the archive in a new tab... not desirable. But if we use just a regular go command, Opus ignores the embedded commands that follow. I imagine that when support for the embedded commands was created, it was probably only expected to be used when opening new file lists (new tabs, new lister windows, etc) since the embedded command feature was created to provide a way to be sure that certain commands operated on the new file list.
So running a plain unqualified go command probably doesn't trap the embedded commands by design.
Also, in the case where you've downloaded a comic archive that contains another FOLDER inside the archive rather then the jpg images right at the root of the archive - the alternate ~smart example above wouldn't work. We'd need some scripting glue to examine what is happening inside the folder, maybe a script could do everything for you to make it smart and smooth.