RTE rules cover the whole napoleonic period, but some theater of operations need some special treatment.
So is the case for Peninsular war and belgian campaign 1815.
What is the pitch ?
French infantry rarely use line formation to attack anglo allied units.
(there is the exception of the formation used by 1st corps at waterloo, huge brigade or division columns of batallion in line).
Line formation was used whith defend orders (as Ferey division covering army retreat at the arapiles 1812).
But RTE gives players liberty to use which formation they want.
First, a friend and me have prohibited attacking or moving in line with french infantry.
But there is an alternative:
-1 to resolve test when a french batallion is in line and with an order other than Defend.
And if testing changing formation when in line whith order different than Defend, use lower quality (exemple Drilled unit use recruit testing column).
Guard units would be unaffected at all.
Players would have liberty of choice, but Attacking in line would be less interesting (knowing that attacking in column would give a +1).
Using the special Ist corps formation attack at waterloo, i think it should be considered a column for resolve test (+1), a line for mouvement, and could not form square.
But could use column or line (choice would be given) to obey attack orders"must do".
For exemple such a formation could behave as a line and not be obliged to charge a non wavering enemy, with the project to fire against it then charge it when it wavers.