Possible to disable power steering on a T?

Of course questioning WHY you would like to do that?
The T has a smaller steering wheel, because it does have power steering.

Now to the technical part: I have not looked at the assembly specifically so it is just a guess, that IF the PS has its own belt driving the pump, you could actually disable it by simply pulling that belt.
I was caught on a lonesome desert road once with an E30 BMW (that was the 80's square 3 series) and got a worrisome noise. Stopped to see a trace of oil squirting out of the steering rack. With hundreds of miles far of any help, ruining the hydraulic pump was not an option. So I found, that there were different belts for alternator + water pump than for the hydraulic pump feeding pressure to the PS. Swiss army knife out and cut that belt. Drove half a year without PS before able to get a new steering rack installed. So far no problem.
HOWEVER: if that belt does serve something else as well, DON'T even think of it.

F.e.: on most cars the dynamo/alternator is on the same belt as the water pump. Therefore when the battery warning light comes on, you must stop. Not for the electric power that is now drawn directly out of the battery, but for your engine not being cooled no more.

 

I had the power rack rebuilt on my T a few years ago. The unit was losing the power assist occasionally, making it a bear to turn the steering wheel at slow speed.
I've been happy ever since the unit was rebuilt. The power assist now functions perfectly, with just the right amount of "feel" on the steering wheel.
I believe the Mondial t's power assist varies with speed - the faster you go, the less power assist. You really neeed max power assist at slower speeds.

 

I think near to impossible without major engineering input - the t used a completely new set-up later largely carried over to the 348.
I would check if your t's steering's variable assistance works as it should. I just recently drove a Valeo t and the steering was pretty nice - no desire to remove the assistance.