Instead of the built-in Execute a Macro action, you can run a macro via AppleScript. As an example, this macro:
tell application "Keyboard Maestro Engine"
set MacroToRun to getvariable "ThingToDo"
do script MacroToRun
end tell
executes this macro:
which produces this result:
With this method, you could set the variable naming the macro-to-be-run however you like, then either replace your current "IF ELSE" based macro with one consisting of this single Execute an AppleScript action and run it as a sub-routine with an Execute Macro action, or just add the AppleScript action in an appropriate location for each macro that sets the variable it uses.