Yep, adding water is a perfectly good solution! You can do it a little at a time until it tastes right and then make a note of however much water that was.

Bypass brewing seems underutilized in pourover -- although it's pretty common in aeropress recipes. Crown coffee has an interesting post about it from a while ago.

Bypass will reduce your extraction and hence efficiency, but that only matters in a commercial setting IMO. That being said, if you want to achieve the same thing without bypass at the end, probably what you'd end up doing is using a longer ratio (more water) and then possibly needing to tweak another variable such as grinding a bit coarser to re-balance the flavor.