Well this has been raised befor eover the years anumber of times but... The way I would do it is to use your paint programme ideally paint shop pro or photoshop or gimp to remove all pixels that match the blue green clolur of the decal sheet. The only problem then is that all the wight decals wont showup. Printing white is difficult unless you have some really high end printing stuff, I supose you dont as you`d not be asking if you did. An Alps printer can do a withe print but these are sadly no longer made and are geting hard to find both working/new and as spares. If you dont want the white decals like the UNSpacy script then no worries, as for the kites just print onto a peice of white decal paper. Better results are from the laser printer decal sheets these are available on Evilbay quite cheaply. If you dont have a good res color laser printer save the file format as graphics shop format and take it to the printers and get them to print it out.
For your interest I use Paintshop pro 9 Photoshop CSV (sometimes) and Serrif Draw and Seriff 3D a cheap scanner and the colour laser printers at work
Generally as a rule I scan em in at a high res and then in my paint programme scale it down to the correct size for the original decal sheet and then go to work on them. I have a programme that converts the jpeg from the scanner into a vector graphics image which scales down with out loss of quaility. This helps so much you can if you like just draw over them using the layers function in a vector format wich is perfectly scaleable. Hope this gives you some insights Im sure that the others here who are into this too will chime in and fill in the bits I missed out etc.