As far as z height for first layer. You can change layer height for first layer in Bambu Studio. Under quality setting, you can set first layer height and first layer line width. If your trying to get more or less squish into the bed, these settings will accomplish this. You can also lower the Elephants Foot compensation setting, also under the “quality” settings.
If you want to adjust flow rate, I believe the SoftFever fork of Bambu Studio, on github, offers some setting adjustment. Maybe someone else can chime in about this?