Not a professional opinion, nor do I speak from experience since I don't have a clitoris, but I can speak about desensitization:
I suspect it is possible, depending on the position of your clitoris in relation to the contact point on the seat (as every one is built differently, you see). But, if this were to happen, you could correct the problem by stopping the activity. Eventually, the sensitivity will return.
One can become desensitized to a number of things: Watching too much tv, eating too much of the food you love, listening to the same song too much... you get my point. If you are really concerned, take this advice: Moderation is the key in all things.
Just an additional note on the matter since I've had a chance to read some of the other comments: Yes, you can become desensitized if you do something too much. I, personally, have desensitized myself to a number of things by participating in them too much. Again, if it happens, just take a break from that activity.
Best to you!