The Transliteration module doesn't update anything on its own. It's the Pathauto that controls that. Just enabling the Transliteration won't do anything.
Pathauto module has a setting for what happens when an entity is updated (
/admin/config/search/path/settings). This means that when you edit existing content Pathauto may change the alias depending on your settings.
You can set it to
Do nothing. Leave the old alias intact. This way you'll be able to edit old content without the alias being automatically changed.
If you need to use some other
Update action setting you'll have to remember each time when editing an "old" node to untick the option
Generate automatic URL alias and use the "old" alias manually.