Ok, I think you can do it without the list widget using this instead of the action-listops:
<$action-setfield $tiddler=<<tid>> $index="mode" $value={{{ [<tid>getindex[mode]compare:string:eq[author-mode]][<tid>getindex[mode]compare:string:eq[presentation-mode]]+[toggle[author-mode],[presentation-mode]] }}} />
The thing thing is, I don't quite understand how toggle works, and I feel either toggle is buggy or the documentation is. If you don't use it with the +[xxx] construction, it will use the entire pool of tiddlers to output at least one tiddler name. But it will put out exactly one tiddler name. And what is the difference inside of a filter between a "list" and a "title list" ?
At a very minimum, this line is grammatically incorrect: " If neither is present, the first parameter takes precedence is added to the list."
(Probably wants an "and" before "is" )