hei
i stripped down the BLM-Project (so it cant be cloned with out weeks off routing U B ;) )
BLM-how-to.zip
and i wrote some explaination... basicly i made a Grid with a center-cross - so a single button-LED-Fottprint can be placed correct to the Rubber-Button-Grid...
you may have to set a a new "zero position off the Kicad Grid" to this crosses when you place the Button-LED-Fottprint on them...
this Grid also have the Holes for the PCB which are needet to hold the rubber in Position..
maybe you find a "Flip-Chip" Variant for your RGB-LED... it would be better... you should not place it on the TOP side off the PCB... because it will illuminate the Neightbar-Button-Rubbers...
The Hole in the PCB where the LEDs shine thru, act as a Light-Shield...
I too have to draw a RGB-LED board (for a other Task, to illuminate a Frontpanel...), since i dont have expierence with that RGB-LEDs... this will take a while... if you found a solution i would copy it from you....
At Kicad 7... didnt know there is a stable out... good to know... will update too (else i cant check your projects)