That is very likely but the murder of those people justified or not would still likely prompt a significant response unless they had settled there without permission or against the advice of the Empire.
That is an aspect to consider though. Was the attacks against the Klingon colonies random acts of cruelty by the Romulans or in response to unchecked Klingon expansion. There did seem to be a period of rapid Klingon expansion in the 23rd century, not all of which was military in nature. I think of the race by the Federation to claim Sherman's planet before the Klingons did. The Romulan response may have been very different. But even that who was going out to colonize these new worlds? Perhaps fundamentalist or the extreme poor? There was clear examples of classiest views even in the 24th century so the Empire might have seen the massacre as bad but just a bunch of undesirables not worthy of a actual full scale war.