This is one of those things I thought might be easier than it has turned out to be.

Basically, I have a carriage which has the driver wear an animated horse attachment. Easy enough, box up a no transfer horse with the carriage.

But I wanted to script it to allow anyone the owner designates to have temporary driving privileges.

Idea one: I would simply toss in a snippet like this

changed(integer change)
{
if (change & CHANGED_LINK)
{
key agent = llAvatarOnSitTarget();
if (agent)
{
if(agent!=llGetOwner())
{
llGiveInventory(agent, "Carriage Horses");
llSay(0,"Find 'Carriage Horses' in inventory and wear them.");
}

et cetera

The problem is that if I give Mr new carriage owner a carriage with a no transfer item in inventory, apparently the carriage balks at giving it out.

Idea Two: Have the carriage rez a temp on rez horse from inventory, then have the horse ask for attach permission following a listen event triggered by the carriage passing the sitting agent's key. I was fair proud of this idea, until I found out a non owner can grant permission, but llAttachToAvatar will still fail for a non-owner. The things one discovers if one actually gets around to reading the wiki:
http://rpgstats.com/wiki/index.php?title=LlAttachToAvatar

Idea Three: Using an offline server to send the sitting agent a horse. I'm here right now, trying to use a HippoTech Update server. But I'm not having much luck there--the script recognizes the new agent, recognizes that it is not the owner, and I pass back a false "old model" to the HippoUpdate. But, nada.

I'll be continuing to think at this, but was wondering if anyone out there had any good ideas.