When machines send packets through L2 to L3, if the L3 forwards the same packet to a different VLAN, it drops the original MAC ID and in turn uses its own (replaces) interface MAC ID in the forward.
No, L2 and L3 broadcast domains are different. The MAC is only used within the L2 broadcast domain. Once the packet has been forwarded to another L2 broadcast domain (VLAN) via L3 routing the source MAC has to be replaced with the MAC of the router that forwarded it to the new L2 domain.
