Some advice that I learned from my dad on these things, he did a ton of research before buying a pair of these:
First off, I hope you got the high-quality ones. Anything under 300 USD will probably break in a year or two (If you use them strenuously)
Second, make sure everything is perfectly symmetrical on the stilts. My dad measured his, found out one was off by a centimeter or two, called the makers, who immediately told him to send it back to be fixed, as that was WAY too off center. It doesn't feel like much, but it makes you walk awkwardly, and eventually kills the tissue in your knees.
Third: Don't make any mods to the size of these things (that would cause any sort of change in the curve in the back). This will not only probably void the warranty, but make them extremely prone to breakage.
And lastly, not advice, but just some experience. I was once running with them down the road, tripped, and fell onto the concrete. It didn't hurt that bad. I'm not saying try to push the limit, but don't be afraid of a close encounter with the ground.
There are lots of ways to modify "power risers" or "Power skip". (I've work with some for Cirque du Soleil and on some movies)
I know that they were used to make the werewolf legs in the first "Underworld".
Basic modification if you are using these stilts for "character" instead of acrobatic, is to remove the fiberglass spring and replace it with a compression spring under your foot going down to the stilts. It makes it work a little like a drywall stilts mechanism and help clean up the back of the leg so you don't have to hide something sticking out of your leg.
Just so you know,there are some places where they sell these stilts in Canada, (Toronto if I remember) so you don't have to order them from over sea, Look for power riser or power skip or do a search for circus stilts.