Hello: I have personally played with softeners that had adjustments for both regeneration and hardness, but on surfing the web, mostly talk is about setting regeneration. Perhaps a bypass is the simplest fix.
The literature will tell you a globe valve is the right item for flow control. I have had good luck with ball valves and no luck with gate valves. Globe valves introduce a lot of friction in the line even when fully open, which is partly why I like ball valves. If using a ball valve, once it’s set, remove the handle and tape it to the pipe. This MIGHT keep people from messing with the adjustment 😉