If you want to 'fool' ( i read "replace" ) the mod 's squares with skirm formations then swop the "#SQUARE36 #SQUARE72 #SQUARE144" in ord.lst with the skirm one's.(#SKIRM36,...).Not entirely sure if this is what you want to do though.
My fault, I wasn't clear enough.
What I want to do is make it so that when skirmishers are selected for formation, the skirmishers now have 2 formation buttons, the line (button position 6 0) for LIGHT and the column (button position 6 1) for SKIRM.
I have just deleted a whole lot of stuff I wrote here because I just found a simple solution to my problem. Strangely enough I do not have to declare the formations in NRES.DAT nor in ORDERS_GRP.LST
These simple lines in the England.NDS give me the options I want (for England anyway).
Strelec_eng(en) Flagonosec(en) 2
LINE 3 #LIGHT36 #LIGHT72 #LIGHT144 1 Strelec_eng(en)
SQUARE 3 #SKIRM36 #SKIRM72 #SKIRM144 1 Strelec_eng(en)