If a creeper is ignited with flint and steel or commands, using the /data command afterwards to modify its ignited NBT tag to 0b has no effect.

How to reproduce:

1. Summon a creeper.
2. Place a command block with the following command in it:

   /data merge entity @n[type=minecraft:creeper] {ignited:0b}

3. Place a button on the command block.
4. Use a flint and steel on the creeper and quickly activate the command block.
   → The creeper still explodes.

Expected result:

Since the ignited tag was manually set to 0b, its value should be 0b, so the creeper should not explode.

Observed result:

The ignited tag is still equal to 1b, so the creeper still explodes.