Mounting a .50 maybe, when they said "armed" I was thinking somthing more substantial, in a turrret at least. But a.50, maybe.
You'd still need major cultural changes in the organization though to make it a standard for all ships.
The CCGS Cowley had two .50s mounted during the early 90. However, there was no real chance of anyone shooting back. Under similar cirumstances, you might be able to get away with arming the fleet.
But the coast guard is not a fighting force, they don't large enough crews to act as a fighting force, and the crews didn't sign up to fight. To turn the coast guard into even the slightest sort of fighting force, you'd have a long road ahead.
I guess it all comes down to needing a clear definition of what sort of force the coast guard would be expected to project.
As far as the actual fitting of guns, machine guns at least, not a problem. Deck space is always at a premium though, but a removable pedestal mount would work. Running comms, also not a problem, could easily be done through the ships telephone system, or even a direct line, quite easily.