You can NAT to any IP address you want, even if it's not on any of the firewall's interfaces. If you do this then you must make sure that the receiving device knows to route back to the firewall for the reply traffic for these IP addresses, i.e. you must add a route on the outside devices pointing back to the firewall for this IP address range. Keep in mind that these devices will then not be able to get to the 'real' 188.8.131.52/24 addresses that exist on the internet.
The firewall cannot NAT to a pool of IP addresses, though. It can do many-to-one NAT and one-to-one NAT but not one-to-many. If you have the same size subnets (which you do, LAN: 192.168.1.0/24, NAT Pool: 184.108.40.206/24) you can create a Netmap object, which will NAT 192.168.1.1 to 220.127.116.11, 192.168.1.2 to 18.104.22.168, etc.
Muchas gracias, su respuesta es lo que buscaba.