That was helpful, thank you. Yes the Overdrive tends to engage way too soon and too often so it often drops the rpms down below where they should be. It doesn't hurt at all to disengage your Overdrive while driving around on city roads, many get in the habit of shutting it off each time they leave home and only turn it back on when they are going to be on the highway for a while.
There's no easy way to change how the Overdrive automatically engages, like changing the Overdrive so it stays off until you turn it on. That involves a bit of wiring with a relay, a simple switch type change won't do it.
So feel free to get in the habit of shutting the Overdrive off after each time you start the engine... doing so won't hurt anything at all.