
Hello Andrew,
You'll need a workflow rule to update the count of edits and a validation rule to prevent further edits.
Workflow rule (pseudo-code):
Evaluation criteria:
IsChanged($DueDate) || IsChanged($TotalAmount)
Update field action:
$C_EditsCount = $C_EditsCount + 1
Validation rule (pseudo-code):
Evaluation criteria:
CurrentUser() <> $ProjectManager && CurrentUser() <> $Manager || $C_EditsCount >= 3 && (IsChanged($DueDate) || IsChanged($TotalAmount))
I hope this helps.
Roland