Invoice Validation and Approval Question

 Hi , 

I would like to know once an Invoice is Approved & Validated what sort of updates(Header/Line/Distribution) could invalidate the approval/validation status of an invoice causing either one of the below or both 

1 - Status to change to Needs Re-validation 

2- Approval to Needs Re-approval

for example we know changing the distribution account only invalidate the status but doesn't change the approval status , but changing the dollar amount would cause both Approval/validation statuses to change , it would be great if there is any documentation that documents the actions that causes the Approval/validation status to change once they are valid/approved .