Modify local traffic policy from CLI or API

As I said, you can do it with "merge" command.

One example.

1.- Take the current config of nodes with "tmsh list ltm node".

# tmsh list ltm node
ltm node N-WEB1_172.16.100.1 {
    address 172.16.100.1
}

2.- Use notepad to duplicate and modify this config.

ltm node N-WEB2_172.16.100.2 {
    address 172.16.100.2
}
ltm node N-WEB3_172.16.100.3 {
    address 172.16.100.3
}
ltm node N-WEB4_172.16.100.4 {
    address 172.16.100.4
}

3.- Verify that the config is well-written and valid (paste config after executing the command and press CTRL+D).

# tmsh load sys config merge from-terminal verify 
Enter configuration. Press CTRL-D to submit or CTRL-C to cancel.
ltm node N-WEB2_172.16.100.2 {
    address 172.16.100.2
}
ltm node N-WEB3_172.16.100.3 {
    address 172.16.100.3
}
ltm node N-WEB4_172.16.100.4 {
    address 172.16.100.4
}
Validating configuration...

4.- Finally apply configuration (paste config after executing the command and press CTRL+D).

# tmsh load sys config merge from-terminal 
Enter configuration. Press CTRL-D to submit or CTRL-C to cancel.
ltm node N-WEB2_172.16.100.2 {
    address 172.16.100.2
}
ltm node N-WEB3_172.16.100.3 {
    address 172.16.100.3
}
ltm node N-WEB4_172.16.100.4 {
    address 172.16.100.4
}
Loading configuration...

5.- Verify that the config was applied correctly.

# tmsh list ltm node
ltm node N-WEB1_172.16.100.1 {
    address 172.16.100.1
}
ltm node N-WEB2_172.16.100.2 {
    address 172.16.100.2
}
ltm node N-WEB3_172.16.100.3 {
    address 172.16.100.3
}
ltm node N-WEB4_172.16.100.4 {
    address 172.16.100.4
}

6. Save current config into the startup-config.

# tmsh save sys config
Saving running configuration...
  /config/bigip.conf
  /config/bigip_base.conf
  /config/bigip_user.conf
Saving Ethernet mapping...done

Let me know if this helps.

KR,

Dario.