Can I replace only one connecting rod?

Unfortunately no - it would be useless to do so .. Engine removal is required so the crankshaft can be removed for machine shop reconditioning .. Cylinder block 'line-bore' should be checked anytime connecting rod breakage occurs .. In other words a complete overhaul or engine replacement is going to be the final outcome 'IF' a successful repair is desired.. For the most cost effective option - Highly recommend installing a good (used) salvage engine..

I agree with that assessment.