Re: looking to cheat the Nikon BDC reticle system.
Short answer is yes you will have to stay with the reticle you choose, but as long as it has any type of multiple aiming points such as the Burris BPlex, Swaro/Kahles TDS reticle, Nikon BDC, all you need is the distance in inches between the different aim points and you put that into the reticle tool. If you do not have the info in the instructions, simply call the company tech rep and ask for "distance in inches" between each aim point.
The exbal reticle tool lists max power and power blocks and you simply plug those in with zero and hit calculate and it will show you the distances of POI for each bar/aim point at that power. Go back in put in the new operationg power, calculate and write those POIs down.
Yes you will have to stay within the practical limits of the ranging and POIs for your respective scope, but lets be honest. If I can take a scope and have preset POIs to over 600-800, then that is great and will work.
Now as to your lack of knowledge on tapered bases. It is really quite simple.
If your scope has 60 MOA of elevation, that is from absolute bottom to top. If you are shooting a bullet that needs 30 MOA in elevation to go to 1000, then if your zero is the optical center of the scope, then you have only 30 MOA up and 30 MOA down.
Scopes almost always are off a MOA or two on the top and bottom one way or the other. The use of a tapered base (which is expressed in MOA) is to allow you to zero your rifle at 100 and have more MOA going up.
Lets say we used a 20 MOA tapered base which is the most common. In our example before, our 100 yd zefo theoretically would be 10 MOA from the bottom of the scope and still give us 50 MOA going up.
You can get 25 MOA, 30 and 40 MOA on tapered bases. Burris signature rings in 30 mm allow you to set 20 MOA in the rings with inserts and up to 40 MOA with the 1" rings.
Hope this helps.