Q:

How to ENABLE touchpad tap-to-click while typing?  Configuration keeps resetting every few seconds

I want to (temporarily) disable the feature that disables touchpad tap-to-click while I am typing on my keyboard to be able to play games that require simultaneous interaction via mouse and keyboard without having to use a physical external mouse. 
In other words, how can I use my touchpad to click things while pressing keys on the keyboard at the same time? 
Everything I could find on Ask Ubuntu so far was the opposite, how to disable the touchpad while typing. 
Some system info, I am running Ubuntu 16.04 and xinput lists my touchpad as 
SYN1B7F:00 06CB:7406 Touchpad

Update: What I tried after reading this post on ElementaryOS. 
First of all, the properties as listed by xinput and synclient:
$ xinput | grep Touchpad
⎜   ↳ SYN1B7F:00 06CB:7406 Touchpad             id=11   [slave  pointer  (2)]
$ xinput list-props 11 
Device 'SYN1B7F:00 06CB:7406 Touchpad':
    Device Enabled (169):   1
    Coordinate Transformation Matrix (171): 1.000000, 0.000000, 0.000000, 0.000000, 1.000000, 0.000000, 0.000000, 0.000000, 1.000000
    Device Accel Profile (294): 1
    Device Accel Constant Deceleration (295):   2.500000
    Device Accel Adaptive Deceleration (296):   1.000000
    Device Accel Velocity Scaling (297):    12.500000
    Synaptics Edges (298):  49, 1187, 48, 850
    Synaptics Finger (299): 25, 30, 0
    Synaptics Tap Time (300):   180
    Synaptics Tap Move (301):   67
    Synaptics Tap Durations (302):  180, 100, 100
    Synaptics ClickPad (303):   1
    Synaptics Middle Button Timeout (304):  0
    Synaptics Two-Finger Pressure (305):    282
    Synaptics Two-Finger Width (306):   7
    Synaptics Scrolling Distance (307): 30, 30
    Synaptics Edge Scrolling (308): 0, 0, 0
    Synaptics Two-Finger Scrolling (309):   1, 1
    Synaptics Move Speed (310): 1.000000, 1.750000, 0.130976, 0.000000
    Synaptics Off (311):    2
    Synaptics Locked Drags (312):   0
    Synaptics Locked Drags Timeout (313):   5000
    Synaptics Tap Action (314): 2, 3, 0, 0, 1, 3, 2
    Synaptics Click Action (315):   1, 3, 0
    Synaptics Circular Scrolling (316): 0
    Synaptics Circular Scrolling Distance (317):    0.100000
    Synaptics Circular Scrolling Trigger (318): 0
    Synaptics Circular Pad (319):   0
    Synaptics Palm Detection (320): 0
    Synaptics Palm Dimensions (321):    10, 200
    Synaptics Coasting Speed (322): 20.000000, 50.000000
    Synaptics Pressure Motion (323):    30, 160
    Synaptics Pressure Motion Factor (324): 1.000000, 1.000000
    Synaptics Resolution Detect (325):  1
    Synaptics Grab Event Device (326):  0
    Synaptics Gestures (327):   1
    Synaptics Capabilities (328):   1, 0, 0, 1, 1, 0, 0
    Synaptics Pad Resolution (329): 12, 12
    Synaptics Area (330):   0, 0, 0, 0
    Synaptics Soft Button Areas (331):  618, 0, 736, 0, 0, 0, 0, 0
    Synaptics Noise Cancellation (332): 7, 7
    Device Product ID (289):    1739, 29702
    Device Node (290):  "/dev/input/event12"

$ synclient 
Parameter settings:
    LeftEdge                = 49
    RightEdge               = 1187
    TopEdge                 = 48
    BottomEdge              = 850
    FingerLow               = 25
    FingerHigh              = 30
    MaxTapTime              = 180
    MaxTapMove              = 67
    MaxDoubleTapTime        = 100
    SingleTapTimeout        = 180
    ClickTime               = 100
    EmulateMidButtonTime    = 0
    EmulateTwoFingerMinZ    = 282
    EmulateTwoFingerMinW    = 7
    VertScrollDelta         = 30
    HorizScrollDelta        = 30
    VertEdgeScroll          = 0
    HorizEdgeScroll         = 0
    CornerCoasting          = 0
    VertTwoFingerScroll     = 1
    HorizTwoFingerScroll    = 1
    MinSpeed                = 1
    MaxSpeed                = 1.75
    AccelFactor             = 0.130976
    TouchpadOff             = 2
    LockedDrags             = 0
    LockedDragTimeout       = 5000
    RTCornerButton          = 2
    RBCornerButton          = 3
    LTCornerButton          = 0
    LBCornerButton          = 0
    TapButton1              = 1
    TapButton2              = 3
    TapButton3              = 2
    ClickFinger1            = 1
    ClickFinger2            = 3
    ClickFinger3            = 0
    CircularScrolling       = 0
    CircScrollDelta         = 0.1
    CircScrollTrigger       = 0
    CircularPad             = 0
    PalmDetect              = 0
    PalmMinWidth            = 10
    PalmMinZ                = 200
    CoastingSpeed           = 20
    CoastingFriction        = 50
    PressureMotionMinZ      = 30
    PressureMotionMaxZ      = 160
    PressureMotionMinFactor = 1
    PressureMotionMaxFactor = 1
    ResolutionDetect        = 1
    GrabEventDevice         = 0
    TapAndDragGesture       = 1
    AreaLeftEdge            = 0
    AreaRightEdge           = 0
    AreaTopEdge             = 0
    AreaBottomEdge          = 0
    HorizHysteresis         = 7
    VertHysteresis          = 7
    ClickPad                = 1
    RightButtonAreaLeft     = 618
    RightButtonAreaRight    = 0
    RightButtonAreaTop      = 736
    RightButtonAreaBottom   = 0
    MiddleButtonAreaLeft    = 0
    MiddleButtonAreaRight   = 0
    MiddleButtonAreaTop     = 0
    MiddleButtonAreaBottom  = 0

So from what I have read, TouchpadOff in synclient and Synaptics Off (311) in xinput should the interesting settings: 0="always enabled", 1="always disabled", 2="disabled while typing"
I tried to change it (only through xinput or only through synclient as well as through both together, several times): 
$ xinput set-prop 11 311 0
$ synclient TouchpadOff=0

However, those settings were not persistent.  Checking the value back immediately after setting it shows the change to 0, as expected:
$ xinput list-props 11 | grep Off
    Synaptics Off (311):    0
$ synclient | grep TouchpadOff
    TouchpadOff             = 0

But just a few seconds later, the values will reset back to 2 again automatically:
$ xinput list-props 11 | grep Off
    Synaptics Off (311):    2
$ synclient | grep TouchpadOff
    TouchpadOff             = 2

Note however that other settings like synclient TapButton3=2, which I use to enable 3-finger-tap as middle-click work fine and do not reset. 
I have no idea what is happening here and why.  Please help me to set this configuration correctly and persistently to be able to enable my touchpad even while typing. 

A:

I can make the touchpad always enabled for the current session, even while typing, by simply killing the syndaemon process.  This automatically sets TouchpadOff=0 in synclient too. 
killall syndaemon

This will not prevent syndaemon from starting automatically again on the next reboot (or login?)  though. 
To disable the touchpad while typing again, you can therefore either reboot or just restart the syndaemon again by running
syndaemon -i 1.0 -t -K -R -d

Again, this automatically takes care of the TouchpadOff=2 setting in synclient by itself.