Depends on the powder. Some powders can have a larger swing from lot to lot. H4350 and Varget are 2 that have huge swings from lot to lot.
I'll try the new lot first to see how fast it shoots with my normal load. Depending on what I get, I will then make an adjustment and possibly re do my load work up from there. I have gained 120 fps with H4350 switching lots when I shot my 260 Rem with 140 VLD's. Since then, I will re verify my load with a new lot. But now, I just buy 2- 8# kegs of same lot so it will last me about a barrel, or about 2600 rounds worth on 16 lbs of powder.