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When editing a default mapping you can only change the Username property.
Username
Custom Mappings
Repository user mappings can be created for a particular repository. Custom mappings work in the exact same way as the default mappings, however custom mappings are only linked to one specific repository.
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This property specifies which repository this mapping refers to. Note that this property is not shown for default mappings.
Username
The VCS username that Continua will match against the current user. If this username is matched against a VCS username then those changesets and checkins will be linked to the current user.
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