Keyboard Maestro Version 7.1 introduced a streamlined way to Get and Set Keyboard Maestro Variables from AppleScript.

snippet.applescript

### Requires Keyboard Maestro 7.1+ ###
 
--- Set AppleScript Variables to KM Variable Name and Value ---
set kmVarName to "My KM Var Name"
set kmVarValue to "TBD" -- default value of KM variable, will be updated
 
tell application "Keyboard Maestro Engine"
 
  ### GET ###
  -- IF KM Variable does NOT exist, the AS Variable will be set to empty string --
  set kmVarValue to getvariable kmVarName
 
  ### SET ###
  -- IF KM Variable does NOT exist, it will be created --
  setvariable kmVarName to kmVarValue
 
end tell

For more details, see Scripting article in the Manual Section.

• All of the below scripts were designed for use with Keyboard Maestro prior to version 7.1, but they will still work with the latest version.
• They present an alternate method.

snippet.applescript

--- Requires KM 7.0.2+ ---
 
--- Set AppleScript Variables to KM Variable Name and Value ---
set kmVarName to "My KM Var Name"
set kmVarValue to "My data"
 
 
tell application "Keyboard Maestro Engine"
  if variable kmVarName exists then
    --- SET KM Variable ---
    set value of variable kmVarName to kmVarValue
  else
    --- Create & Set KM Variable ---
    make new variable with properties {name:kmVarName, value:kmVarValue}
  end if
end tell

snippet.applescript

--- Requires KM 7.0.2+ ---
 
--- Set AppleScript Variables to KM Variable Name and Value ---
set kmVarName to "My KM Var Name"
set kmVarValue to "TBD" -- default value of KM variable, will be updated
 
tell application "Keyboard Maestro Engine"
  if variable kmVarName exists then
    --- GET Existing KM Variable ---
    set kmVarValue to value of variable kmVarName
  else
    --- KM Variable NOT Found ---
    set kmVarValue to ""
    -- Optionally, throw an AppleScript error --
    error "[ERROR] KM Variable '" & kmVarName & "' was NOT found."
  end if
end tell