It is actually a bit of a long shot that we are related. I have been told that my great grandfather was an RIC officer and I know that my great grandmother's family were in Granard. The dates of this match the dates of your ancestors' time there. I was never told the name of my great grandfather - it's shrouded in mystery - and my grandmother seems to have taken her mother's family name.
Also I was going through some documents recently and found a Mrs Cosgrove or Cosgrave apparently living with or lodging with a relative in the family house - until 1945- so I thought that might be a connection too.
You seem not to have done much investigation into any possible Granard relatives. I am interested in the town itself as well as doing genealogy there.
Is it OK to ask what your RIC ancestors looked like to see if there is any resemblance? It's a long shot I know but might be quite interesting.
I am in the Glasgow area too.