All Caps font by custom parameter

I have seen Creating an all caps font but would like to make an uppercase version of my font through a parameter instead of deleting my lowercase and keep two files.

I am surprised that neither Reencode Glyphs: A = 0061 nor Reencode Glyphs: A = 0041 , 0061 works. Both remove the uppercase A.

Is there any way to do this?

Do I need to create a component glyph of A?
Let’s call it A.comp:
Reencode Glyphs: A.comp = 0061

Is this the best solution?

You need to remove the lowercase first: