I played a game that implemented something like this. A player could have 32 buffs simultaneously, and on release there were fewer than 255 unique buffs. The id for each buff was stored in one byte and was bundled along with all of the other buffs into a much larger packet which also contained other player data.

The game later surpassed 255 unique buffs. Rather than change the packet structure, they repurposed a group of 64 bits which had previously been padding. Each buff id could then be unpacked by using the nth pair of bits from the block of 64 as the two high bits, and tacking on the original byte as the lower eight.

Good point. We have an open req for a data engineer, so I'm sure it'll be fine.