Asus AC66U NAT Configuration Help

Hi all,

Scenario:

Router: Asus AC66u with last Merlin's firmware.
ISP: 1 direct connected ip + 64 ip subnet (for example 5.5.5.5 and the 64 ip subnet:
82.77.222.128/26)
Lan: 10.10.10.1-10.10.10.255

How can I make the lan ip 10.10.10.55 to be translated(nat) for example as 82.77.222.129?
I mention that I don't want to disable the nat and and configure my lan with 82.77.222.128/26, all I want is to know how can a specific intra LAN ip to be custom translated?

Thank you in advance guys