I have a harp. It's a pretty thing. Sits by the front doorway of my house. But it doesn't have any sharping levers. If I wanted to add a few levers, so I could play in another key or two, would this be a difficult task? I reckon sending it off to have them installed would be a little expensive (and risky) given the size of the thing.
What kind of harp is it? Does it already have bridge pins? What kind of levers are you considering?
Installing sharping levers can be a pain, unless the holes are pre-drilled. Not so much "hard" as "fiddly," as you have to be very precise. Some harps (such as the basic Harpsicle) can't take levers, so it's important to know what you have.
You might consider asking here:http://www.harpkit.com/mm5/merchant.mvc ... de=contact
Even though you're not working with one of their kits. They could tell you what's involved. Jerry Brown 's a big proponent of folk harps and folk harpers, and I'm sure he'd be willing to offer you some advice.
They have a bit of a video here:http://www.harpkit.com/mm5/merchant.mvc ... ode=levers
Talks more about lever types than about installation, though.
BTW, most luthiers or instrument technicians should be able to install levers on a harp. If you have a music shop with a good technician near you, there's no need to ship the harp off to have levers installed. Cost varies, but it was about $15/lever (including the lever itself and the labor) when I had Loveland Bs put on my Ravenna a few years ago. The Ravenna has the holes pre-drilled, though, so it's a little cheaper in that regard.
You'll want to seriously consider how many levers you want, and which ones (and whether you really need them at all). For the greatest degree of chromaticism, you'd have levers on all strings and then tune to Eb, but there's a real trade-off in tone, even with the best levers. If you play primarily folk music, I'd go for Cs and Fs...possibly Bs if you also like to play things like hymns and such (F is a useful key to have available). Beyond that, it's probably not worth the cost and effort, unless you want to play classical or contemporary music.
Bear in mind that you don't need levers if you just want to play in different keys. You can always retune. Wire harpers get very quick at that, as levers aren't particularly satisfying (or traditional) on wire harps. Levers are useful if you need accidentals, or if you play in so many different keys that retuning is impractical.
BTW, I'd suggest moving that harp away from the front doorway. They're more susceptible to changes in temperature and to drafts than most instruments.