David,
The update process across wikis is like being able to update all word documents on your hard drive. Here some designer type notes, the first components you need are;
- Create a set or bundle of the items you wish to distribute to more than one wiki
- Get each wiki to subscribe in someway to that bundle of tiddlers
- The get it to automatically collect the tiddler bundle when changes occur to that bundle
However you do not have access to the server backend on tiddlyspot so the only way to trigger the update is when you load the specific instance of the wiki in your browser. Then perhaps a button or startup action could import the tiddlers then. This becomes just in time updates, just as you go to use the wiki it searches for updates.
I have being trying to establish a way to set up an import from a saved url method with no luck so far but this would help.