Try this:
<$list filter="[[$:/config/ViewToolbarButtons/Visibility/$:/core/ui/Buttons/edit]get[text]!match[show]]" emptyMessage="""
<$action-setfield $tiddler="$:/config/ViewToolbarButtons/Visibility/$:/core/ui/Buttons/edit" text="hide"/>""">
<$action-setfield $tiddler="$:/config/ViewToolbarButtons/Visibility/$:/core/ui/Buttons/edit" text="show"/>
</$list>
Notes:
* if the config tiddler does not exist or has content matching "show", then the "hide" action is performed
* otherwise the "show" action is performed
Also, you can make the code more compact, by defining the config tiddler title using a macro
and using a filtered transclusion instead of a $list widget to set the content to show or hide, like this:
\define config() $:/config/ViewToolbarButtons/Visibility/$:/core/ui/Buttons/edit
<$action-setfield $tiddler=<<config>> text={{{ [<config>get[text]!match[show]then[show]else[hide]] }}}/>
enjoy,
-e