Hey @delleigh
At the moment it is not possible to add a comment or note directly to a salary increase. However with our upcoming tool Compensation Management, they are aware that this is a requested functionality that would benefit a lot of customers. Therefore it is eventually in our plans to allow for reasons to be put in with salary changes, however I cannot give you an exact timeframe on this. If you would like to know more about this feature, I would suggest reaching out to your Growth Manager.
As you mentioned, the main workaround at the moment would be to use the Notes tab or to create attributes to track this information. If there is anything else I can help you with, please let me know.
Best regards,
Conor