The system tiddler you want is:
$:/config/SaverFilter
The default contents are:
[all[]] -$:/HistoryList -$:/StoryList -$:/Import -$:/isEncrypted -$:/UploadName -[prefix[$:/state/]] -[prefix[$:/temp/]]
and defines a filter that produces the list of tiddler that are to be checked for changes. The filter starts with "[all[]]", which includes all *real* tiddlers (i.e., not shadows). It then excludes specific named tiddlers and tiddlers that start with special names like $:/state/ and $:/temp/.
Anything tiddlers excluded from list will NOT cause the document to be considered 'dirty', even if the content of those tiddler have changed.
To exclude your own tiddlers, simply add more filter runs to the end. Make sure to use the "-" prefix so that your matching tiddlers are removed from the list, instead of being added.
enjoy,
-e