Giving zombie villagers multiple apples or curing them multiple times?

Solution 1:

No, giving more than one golden apple has no effect.
However, performing multiple dezombifications results in better trades.

According to Minecraft wiki:

The newly-cured villager, if it had a profession prior to being zombified, offers a large discount on trades to the player who administered the cure. The discount from curing a zombie villager persists permanently.

If a villager is cured more than once, its discounts increase until the price reaches the minimum of one emerald.

As an extra:

Villagers around the cured villager are also affected. In Bedrock Edition, villagers in a range of 16 blocks in a cube surrounding the cured villager also offer a small discount proportional to the number of cured villagers (up to 10).