Yes, I have done it quite often. The first thing you need is graphics software. The gold standard is Photoshop, but it is very expensive. For resizing decals that are scanned from an existing graphic, not much is needed, so a relatively inexpensive graphics program is usually adequate. I believe one comes with Windows. You need to compute (easy grade school math) the resizing percentage, then resize the scanned file by that much.
Then, you need to print it on inkjet paper (clear). This is easy for dark decals over light colors (NWA markings are mostly in this category). Making white decals is a whole different ball of wax).
Then you must coat the decals to make them waterproof. However, they must be completely dry first. Depending on the printer, this may take 3 to 4 days. I use Testors glosscoat myself, but I have tried several other clearcoats with good success.
You will have to cut out each decal carefully, since this process makes the whole sheet into one decal.
I saved one airliner kit that already had NWA markings. I now always scan decal sheets before using. During application of the kit decals, I ham-handedly ruined one of the long side stripes. No problem- I printed and coated a replacement. Asked my friends to tell me which side was homemade- they couldn't tell.