I don't know how I could have missed this trick, and I'm sure the pros have known about it for years but I just added more panels to existing aircraft.

For example, I have the Beech Baron with the MS and Tipsters RTW1 and 2 panels.  3 panels for one AC.  MS and RTW1 were just backups taking up space.  A little editing produced this:

[fltsim.0]
title=Beech Baron 58
sim=Beech_Baron_58
model=
panel=
sound=
texture=
kb_checklists=Beech_Baron_58_check
kb_reference=Beech_Baron_58_ref
atc_id=GP009
ui_manufacturer=Beechcraft
ui_type=Baron 58
ui_variation=RTW Final Panel
description ...

[fltsim.1]
title=Beech Baron 58 RTW1
sim=Beech_Baron_58
model=
panel=1     <-- Points to Panel.1
sound=
texture=
kb_checklists=Beech_Baron_58_check
kb_reference=Beech_Baron_58_ref
atc_id=GP009
ui_manufacturer=Beechcraft
ui_type=Baron 58
ui_variation=RTW Original Panel
description ...

[fltsim.2]
title=Beech Baron 58 Default
sim=Beech_Baron_58
model=
panel=default   <-- Points to Panel.default
sound=
texture=
kb_checklists=Beech_Baron_58_check
kb_reference=Beech_Baron_58_ref
atc_id=GP009
ui_manufacturer=Beechcraft
ui_type=Baron 58
ui_variation=Microsoft Panel
description ...

All you have to do is point the panel entry to the right place and change title and ui_variation.  I haven't tried it yet but I'll bet I could alias the panels too.

Good one!

All the following entries can be amended to address different features:

sim= (air file)
model= (Visual display of the aircraft)
panel= (you've sussed this)
sound= (Self explanatory)
Texture= (The one most people are aware of)

My 747 uses three different panels, 2 soundsets, 2 models and 5 textures.

The reason for the 2 models (if you were wondering) is one is a cargo variant with a different panel, sounds (P&W engines rather than RR)  and of course textures.