Scope help needed

Really no different than you describe (although don't know if the same software will help). A good FFP scope's reticle will keep the holdover the same between magnification changes. The range card (set up for the new scope) will still apply but will be useable at 'any' magnification. Always best to derive the range card from actual use. I set out targets at distances appropriate for the rifle and make my notes from shooting them. 
 
You will still use the lower power to open up your field of view at any point needed, but the reticle will appear smaller on an FFP because the POI never changes. I have Hawke Sidewinder 6-24x56 FFP and an Aztec Emerald 6-25x56 FFP plus Hawke 8-32x56 AirMax SFP scopes. Honestly, and after shooting tens of thousands of pellets through each at this point, I don't really have a preference. The 2nd focal plane reticle is easier to see when shooting out really long distances but I really like the convenience of having the POIs always consistent with the reticle that the FFP offers, and rarely (never to date because of my set-up) have an opportunity to shoot beyond 100 yards, so reticle size is not an issue for me....