Two ideas. either one or both.

1. Lilypads can be bonemealed to spawn an adjacent one if there is free water source block directly adjacent.
2. Bonemealing sand/dirt/etc in 1 deep water in a swamp biome a lilypad has a chance of appearing similar to how coral can appear in a warm_ocean when specific ground materials are bonemealed.

Mostly I want this because being renewable through AFK fishing is terrible since its not even a junk item and I am planning a skyblock run and would like some way to acquire and renew lilypads.

This would make more sense to add to betterBonemeal in carpet-extra.
I will try to make a pr (on the first idea probably, makes more sense if its in the same rule that makes cactus and sugarcane bonemealable)