Can you overassign combat damage to one unit to avoid killing another unit (like Ekko) when blocking with multiple units?

Ruling: You cannot overassign combat damage to blockers. You must assign exactly the amount of damage needed to make each blocker lethal before moving to the next one.

Nuances:

• You can overassign damage to the last unit in the blocking order
• This ruling was confirmed on stream but the CRD (Comprehensive Rules Document) has unclear wording on this issue