Use “xset m val val” or “xinput –set-prop device property value” to change the mouse speed.

xset m will be applied to all pointing devices, while xinput lets specify it. No need to logout since the values are applied on the run-time.
To find the device and the property to change:
xinput –list –short >> will return a list of the devices.
xinput –llist-prop xx >> will return the properties list with its ids.
Then >> xinput –set-prop deviceId propId value >> will change the property value