Cossacks in Lasalle: An optional rule

Irregular units (Cossacks, Kalmuks or Bashkirs) in Lasalle can not initiate combats against regular foes.
The reason behind, according to Sam Mustafa, is that these units were not used in formal battles, but only in pursuits, ambushes and the like. Their only utility is to add points in the 'Pursuit and Victory' step during the Army Morale Check and Victory (p. 67 of the rule-set) along other 'Pursuit' cavalry units like hussars, chasseurs, chevaux-legers and similar.
During game play, the only use I found for the Cossacks is to use they to avoid the fall back of enemy units, placing them in the rear of the defending enemy. However, I think that these cavalrymen do not remained iddle during the battle, but were seeing always to make opportunist attacks against un-warned and surprised enemy units, such as march formation columns or convoys.

My proposal (posted to the Lasalle Forum) is the following:
1) Irregular cavalry units may charge enemy units standing in 'march column' formation.
2) Irregular cavalry units must to pass a 'Discipline' test to initiate the charge.
3) If routed in 'decisive combat' the irregular cavalry unit is immediately broken.

In Lasalle, the units in march column formation can not fire (although they can try to change formation) and halve their combat dice so they are potential targets for opportunist attacks. However, these attacks were not automatic -a discipline test is required- and were usually unsuccesful -the irregular unit risks its dispersion- but succeeded in occasions.

I think that in this way the opportunist and volatile behavior of these units is well simulated. At a minimum they'll have a chance to see action!