As long as the kolsch yeast fermented out completely, you won't hurt anything by lagering it. Lagering is just cold storage, it doesn't matter if you used ale or lager yeast prior to this step. I've found that lots of my beers have been improved with extended cold-aging. Beers fermented with neutral ale yeasts even come out tasting like lagers.
Seeing as you fermented with a kolsch yeast at low (for an ale) temps, I'll bet cold aging it for a month or two would make it taste an awful lot like the light lager you were aiming for.