Where or when are L2(ethernet) src/dst addresses changed during forwarding or local-out?

[Youngmin Kim]

Where or when are L2(ethernet) src/dst addresses changed during
forwarding or local-out?

In linux kernel about network, Which functions and forwarding phases
are
related above?

forwarding phase : 

1. 
packet --> NF_IP6_PRE_ROUTE --> decision of forwarding or local in
--> (if forwarding) NF_IP6_FORWARD --> NF_IP6POST_ROUTING
2. 
packet --> NF_IP6_LOCAL_OUT --> routing --> NF_IP6_POST_ROUTING

Thank you!!