Sales Manager approve or decline the sales rep data at Sales Center level. So just create a line item(Approve/Declined?) in the Sales rep input module and get the data from the Sales Center Approval/Decline Module.
Use dynamic cell access to restrict the data input, if the sales manager accept the data it should be read access only, if not then write access and also use conditional formatting to highlight
Alternatively you can use the new workflow tool that pushes the request to a child list that has a module that overwrites the value. Thus sending an email to the sales rep and gives them a task to complete.
Also setting up a boolean on a view that allows for the Sales Rep to review any submitted request that has been declined, which has their original value and the new value they would like to replace using a if/then against an approval by the sales manager is another method.
Specifically for notifications outside of creating a module that appears on all of the dashboards within the model that has 'outstanding actions' and summary values, you would need to utilize the workflow feature to generate an email.