My 2c worth - I have a couple of different lengths of paracord with loops at both end for tillering, and I make a new string for each new bow once they're tillered to brace height.
The paracord tillering strings support bows of any weight well past 200lb, and you don't usually have loads of different length staves in the first place - most of the time you cut a piece to length depending on what you're making. That means you can have about 3 different tillering strings of paracord and you never need to keep adjusting them. The exception to this is when you have to pike a bow, or you're working with something unusually short/long.
If you can make a Flemish twist bowstring with two laid-in loops, you also shouldn't have a problem with the actual bowstring. After a few practice attempts, its fairly easy to knock up a finished bowstring in about 5 minutes without even using a jig of any sort, and if you have a way of knowing how long to make a string depending on the finished bow, again there's no faffing about with changing lengths etc.
To clarify, this is my procedure:
1. Cut stave to normal length (77" for example if making a self Yew warbow)
2. Select paracord tillering string for 77" stave
3. Tiller to brace height
4. Make Flemish twist string with loops at both end for 77" bow using formula for strand length
5. Fit string and brace bow
6. Tiller to 29.5", watch bow explode in spectacular fashion, swear loudly and return to step 1.