I've thought about doing it, but it's almost impossible due to the possibility of deeply nested tags and snippets called in the code of other snippets and plugins, often using variables instead of names.
For example:
$result = $modx->runSnippet($snippetName, $fields);
The real name of the snippet being called might be in the $scriptProperties array (sent in the snippet tag), a System Setting, User Setting, Group Setting, or Context Setting, or in an included file.
FYI, you should never, ever, change the ID of any object in MODX. That ID could be used in a variety of places and changing it is a recipe for a disaster that would be virtually impossible to fix.
If you can explain why you want to change an element's ID, we might be able to suggest another way to do what you want.
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