Actually, adding/modifying an item it builds into is a change to Hexdrinker, because it changes it's power value at certain game points.
Back when Hexdrinker was exclusively a T2 item with no upgrade path, it was considered very weak. Mainly because while it made it nearly impossible to lose lane, you would lose a ton of pressure come mid/late game as you either had a T2 item stuck in your inventory, or would have to sell it and take a large loss in gold efficiency. By the way, the old Hexdrinker was even more powerful/gold efficient than the current one is.
Once it got an upgrade into old Maw, it was better, but Maw still was pretty situational because all of it's power was tied into your being low on hp so that the AD based on missing hp could be triggered. This meant it was a situational pick, and couldn't be depended on 100% of the time.
Then we got current maw. It got like 20 more MR, a scaling shield value on MR, to give you a stronger shield, which is further amplified by the very MR you have to make it protect you more, made it a much stronger protective item against APs, but they also gave it one of the most valuable stats in the game, armor pen. Point for point Arpen is FAR more valuable than AD, and THEN they also gave it Lifeline, which means that Maw still has it's old strength of becoming stronger if your hp gets low, it just was changed from more raw AD to sustain and AS.