Just to check but assume that it's O.K. and allowed to assign the SK bases to units and then deploy the units as irregulars?
For example, the Prussian Landwehr are Unpredictable/Am/SK1. Normally they can't deploy as irregular as they would need to be SK2 or above. However, if they were assigned one of the extra SK bases in a Prussian list then they could take advantage of the irregular deployment rules.
I ask as I'm working on basing figs and wondering if it may be worth using my extra Landwehr figs as an irregular unit.
They may be a useful option for a Prussian force. I have found Irregular have actually been actually quite useful in the Ottoman army, as long as there are woods for them to play in. :)
Mark