Alow parmterisation for value, footprint etc

I'm currently considering the need to change most 2-pin passive components on a PCB from size 0805 to 0603.

Suppose the "Footprint" field of a schematic symbol allowed parameters, e.g.
   {my_def_2pin_footprint}
Where the use of '{' ... '}' indicates parameter value substitution is desired.

Then, in the rough equivalent of a "Spice Directive" I write
   .param my_def_2pin_footprint = SJB_001_LIB:0805_HAND_SOLDER

This feature is very useful in LTSpice, and I think it could be useful in KiCad.

Also, allow comments preceeded by maybe ';' or '//'. Thus: I might have
   //.param my_def_2pin_footprint = SJB_001_LIB:0805_HAND_SOLDER
   .param my_def_2pin_footprint = SJB_001_LIB:0603_HAND_SOLDER