That is correct. I'm sure Hodgdon strives to keep these powders the same under matching test conditions, but other factors, like how easily the vibration of travel packs them down, can also become a factor. So you treat it like any new component, cutting the load back and working up toward your previously established load. The only exception I make if for new lots of match bullets from small, domestic companies like Sierra, Hornady, Berger, Nosler, etcetera, for which, if it is the exact same bullet product number, I've yet to detect a difference in pressure or velocity from lot to lot. Big companies I am less sanguine about. They sometimes outsource their bullets and they aren't always exactly the same from on lot to the next. We had someone find different lots of 0.355" and 0.356" diameter bullets identically packaged by Remington for 9 mm pistol as 0.355". He contacted them about it, and they said they couldn't be expected to change packaging for a difference that small. So I'd work back up with Remington or Winchester bullets and with any kind of bulk bullet purchase except for cast bullets for light target loads.
That said, it only takes about 3-4% charge weight adjustment to compensate for a 6% burning rate difference, if all else stays the same. All else probably doesn't stay exactly the same, though, so I use Rocky Raab's old rule of thumb to reduce an established, non-maximum (for the particular rifle) load by 5% when changing only a single component. If I change two or more, then I apply the full 10% reduction. If I were changing the primer in a very small case, like a 22 Hornet, I would also go with 10%.
