No! Just no!
Trying to slow down a kart by limiting throttle travel will just burn out any clutch you have due to slipping. Especially a centrifugal clutch. The engine doesn't get up to the required RPM's to lock up the clutch. All you ten have is slipping and burning.
The safest and best way to reduce speed is to gear lower. That means changing sprocket sizes. You could also get larger rear tyres which essentially is the same as gearing lower
There are all sorts of machines with all sorts of different types of clutches all over the world that have probably never been put to full throttle.
And they work just fine.
I have decades of running snowmobiles with cvt's.
There are constant situations of moving the sleds at less than drag strip accelerations, on-off trailers, across sheds and yards, road ditches, etc.
Sometimes simply riding slow to enjoy the scenery.
Often times new riders have to be encouraged to give more take off throttle to help out the clutch to engage completely, but it never comes to applying anywhere near full throttle.
Your warning of not limiting the throttle so much as to affect clutch engagement is valid, but to call out for absolutely no limiting is just wrong.
So, if limiting throttle movement solves the problem, by all means do it.
Just make sure there is plenty of throttle to get the clutch engaged without drama.
And understand that throttle limiting is still different than ground speed limiting.
