Good pictures - yes, a knarp is just a screw-on cable end that you can take on and off by tightening or loosening the set screw. There are many different types - they actually do sell some specifically for brake cables. They tend to work, but do not always fit inside the brake arm sleeve very well.
Yes, soldering works fine if you are careful and do good surface prep. The can look very clean and very original if you get it right.
The nipple crimp method is where you use a Bell Systems Type D crimper tool (usually a few dollars on eBay, I think mine was like $15 shipped to me) to crimp a spoke nipple into place on the cable. Once you get the hang of this, you can get the crimp very tight and just as solid as a good knarp. The plus of the nipple crimp is that the spoke nipple will often fit into the brake arm sleeve well.
The most important thing to remember is these cables are of fixed length. You need to get the length right for them to work well. Measure twice, crimp/solder/knarp once.
I would not go back and undo everything if you've already put standard-style calipers on the bike. They work fine. But no need to throw away your Raleigh calipers if you want to use them later.