Detecting touch_start problems

I have a prim that is set to sit on touch. Once the avatar is sitting on it, it would be very helpful if I can detect if the avatar clicks on it again.

Is it possible from LSL to change the sit on touch to touch after the avatar sits on it?

Yes, when the AV touches it to begin with, after making them sit on it, have the script go to a different state, such as SittingOnPrim. Then you can use a new touch start command to do what ever you like.

Here is an example for you:

default
{
    state_entry()
    {
        llSay(0, "ready");
    }

    touch_start(integer total_number)
    {
        llSay(0,"they are now sitting on me");
        state SittingOnPrim;
    }
    
}
state SittingOnPrim
{  
    state_entry()
    {
        llSay(0,"I am in the sitting on prim state waiting for another touch");
    } 
    touch_start(integer total_number)
    {   
        llSay(0,"I am now doing another touch activated thing");
        state default;
    }
}

I don't think that you get a touch event when a prim is set to sit on left click is left clicked, and I don't see a way to change that behavior from a script... so the sitter would have to right-click and select Touch from the pie menu.

Boss is right. So you don't need an extra touch event. Just touch to sit and then right click/touch to activate. But what I do in my teleport bubble is touch to sit and then "changed" will detect the sit and activate the teleport.

Im trying to get the state thing working but no success.

I have the prim w/ left-click set to sit.

changed(integer change) { // something changed
        if (change & CHANGED_LINK) { // and it was a link change
            if (llAvatarOnSitTarget() != NULL_KEY) { // somebody is sitting on me
            
               
                //enter sitting state            
                state sitting;
            }
        }
    }


state sitting
{
    //touching the prim should mean the avatar wants off
    touch_start(integer total_number)
    {
        //unsit the avatar
        llUnSit(llGetOwner());
        llDie();
    }
}

But even with this, the left-click is still only doing the sit action.

There are a couple of problems. Number one, your if test is not working. You can see it by using the script with debug llOwnerSay's in it. Number Two, Left click will still always do just sit. After you are sitting, you will have to right click and then pick "Touch" and it will unsit you and the object will die.
EDIT: So you have three choices. Left click sits you and then right click/touch unsits you and dies OR,
Right click/sit and then left click unsits you and then dies OR,
Put in another changed event and then you left click sit and when you stand up the other changed event fires and the object dies.

default{
	changed(integer change) { // something changed
		if (change & CHANGED_LINK) { // and it was a link change
			if (llAvatarOnSitTarget() != NULL_KEY) { // somebody is sitting on me
				llOwnerSay("if test");
				//enter sitting state            
				state sitting;
			}
			else{
				llOwnerSay("else");
				state sitting;
			}
		}
	}
}


state sitting{
	state_entry(){
		llOwnerSay("sitting");
	}
	//touching the prim should mean the avatar wants off
	touch_start(integer total_number){
		//unsit the avatar
		llUnSit(llGetOwner());
		llDie();
	}
}