At an RCCA/AMA rules contest, putting tape on the streamer like that is going to be frowned upon. I suspect that kind of taping won't help much anyway, the streamer will just break at the end of the tape (even with the tapered down effect), and, frankly, flying around with a visible chunk like that is asking for someone to take a swipe at it, and that's not good. I frankly prefer the string to break and have someone take the whole thing rather than leaving a couple of feet, since I'd really prefer other guys not be taking shots that close to my plane if I can help it.

(of course, going for the scraps is part of the game. I do it, and I expect others to do it. I'm just saying that setting myself up as a target isn't what I want to do)

And again, at most contests, the CD supplies the streamer material, or at least makes sure everyone is using the same stuff, which should mean streached the same as well so it comes out roughly the same length. There isn't any real advantage to pre-streaching, except that it allows you to get more streamers per roll of material (sometimes, quite a lot more), and it streaches less in the air, which makes it less likely that you can get a few feet cut off and still land with over 30' of streamer.

A while back, I'd tie the streamer on to the string, then put a very small bit of tape around the knot, which helped keep the streamer from tearing off in flight or on launch. But I pretty much stopped doing that a while ago, since just using proper technique and taking proper care of your streamers is usually good enough. A lot of guys who have constant problems with streamers falling off just aren't taking care of their streamers.