Modify Region table via REST

Yep, you have to supply the entire region member list each time, so if you want to delete one, you have to basically send the entire list again without the member you wish to remove.

Another option is to use a CLI script to do this:

cli script addRegionMemberSubnet {
proc script::init {} {
}

proc script::run {} {
    if { $tmsh::argc != 3 } {
      puts "a region name and a subnet must be provided"
      exit 123
      }
      set zero [lindex $tmsh::argv 0]
      set RegionName [lindex $tmsh::argv 1]
      set Subnet [lindex $tmsh::argv 2]
      puts "tmsh::modify gtm region $RegionName region-members add { subnet $Subnet }"
      tmsh::modify gtm region $RegionName region-members add { subnet $Subnet }
      exit 0
}

proc script::help {} {
}

proc script::tabc {} {
}
    total-signing-status not-all-signed
}

You can then run this from REST using the payload format of

{"command":"run","utilCmdArgs":"addRegionMemberSubnet Test_Region 1.1.1.1/32"} 

on the URL of

https://192.168.1.1/mgmt/tm/cli/script 

I hope that helps.