This is not strong request, just a proposal because the same thing can be done by configuration file.

It may be useful if users can have his command line options.

For instance.
<CommandOptions>
  <CommandOption>
    <OptionFlag>m<OptionFlag>
    <OptionName>isMC<OptionName>
    <OptionType>Bool_t<OptionType>
    <OptionInitialization>false<OptionInitialization>
  </CommandOption>
  <CommandOption>
    <OptionFlag>t<OptionFlag>
    <OptionName>TriggerType<OptionName>
    <OptionType>Int_t<OptionType>
    <OptionInitialization>0<OptionInitialization>
  </COmmandOption>
</CommandOptions>

Then user can change the variable with command line option like
./megframework -m -t 2;

Then builder creates new method.
(Bool_t) MEGAnalyzer::GetisMC()
(Int_t) MEGAnalyzer::GetTriggerType()