I'm looking after editing the intro screen of Pokémon Blue version with Pokémon Green version's intro screen.

Someone told me to use an Hed Editor. (I'm using Hex Editor 3.x)

When I open the Pokémon blue rom with Hex Editor, I don't know what to do next.

Can anyone help me?

I've heard from a couple of people around here that it's compressed, So you might have to circumvent the compression for the game's border GFX.

Good luck trying to uncompress!