ContentSync will save certain settings after a push. These settings can be cleared but they are created to ensure syncs stay consistent as designs may change.
By default a layer's content key is the layer's name. However, once a design is synced, the content key used to sync is saved to that layer. This means that future layer name changes will not update the content key.
Once a layer has been synced, a green checkbox will appear next to the key. This key signifies that the current key has already been synced and is mapped to the spreadsheet.
If a key that has already been synced is changed, it will show up as an undo icon until it is synced again.
Clicking on the undo icon will present the options to restore the previous settings or clean the setting.
If settings are changed such as key prefix or suffix, you may want to reset all the saved settings across a file. Without doing this, previously synced files will not use the new file settings.
To do this, go to Project > Settings > More Settings
These options include clearing all the saved key settings or completely resetting all layer settings (enable/disabled type keys and overrides).