Normally, you can summon entities and give them custom nbt with /summon. However, when you try to put in a custom value for FireworksItem, which determines things like explosions, it gets deleted when the firework is summoned, and so the rocket doesn't explode.

I am testing this with the command

/summon minecraft:fireworks_rocket ~ ~ ~ {Life:1,LifeTime:50,FireworksItem:{id:"minecraft:fireworks_rocket",Count:1b,tag:{Fireworks:{Flight:1b,Explosions:[

{Type:1b,Colors:[I;3887386,11743532],FadeColors:[I;3887386,5320730,2651799]}

]}}}}

which makes a rocket with the entity data at the bottom