I hadn't even thought of that, but you're right, not all rides offer swaps, there's a list somewhere. It may well be TSM doesn't offer swaps which sort fixes the whole issue. I'm not sure if they even offer swap for rides with no height restrictions now that I think about it. I'm going on our experience and since my grandson is very tall for his age, he qualifies to ride things we don't think he's ready for- but it's true, if they don't offer a swap, you can't get one obviously.
But we've just never had a problem getting a swap on those rides where he met the height restriction. And since they have it in their policy, they have to give them when requested. I don't recall offhand if we've ever tried one that didn't have a height requirement, so I have no idea if they actually have them on hand or not.
I don't think it's a matter of capability, it's just do they have the swap tickets on hand at rides with no height requirements?