Can I add elbows to move a b-vent exhaust?
Do a quick search online for the brand and model of the water heater. Most manuals for install are available online, but of course this will depend on the age of the unit. The manual (in most cases) describes the limitations of exhaust pipe distances and in particular the inclusion of elbows in the flue. It is important to check as elbows reduce the ease of flow and will effectively reduce the capacity of the exhaust and distance the flue can run.

So worst case it can make the installation unsafe and it is right to confirm with a professional or the manufacturer.