Per the SDK documentation there is a LocalVars section in systems.cfg that allows for storage of L:vars to be used in the next load of the aircraft, which are saved in states.cfg.
The syntax, per the SDK is this:
[LocalVars] LocalVar.0 = my_custom_lvar LocalVarDefault.0 = 666 LocalVar.1 = my_other_custom_lvar LocalVarDefault.1 = 999
However, in the .FLT files and states.cfg, the format looks like this:
[LocalVars] my_custom_lvar = 666 my_other_custom_lvar = 999
Are both syntaxes valid or should we use the first one?