ROM Hack Editing Pokemon Types

[Rokku]

What software can be used to edit a Pokemon's type?

I'd like to change some types around like the "big boys" do, like making Electivire Electric/Fighting or making Gyarados Dragon/Water.

 

[twistedfatal]

check my topic my tool allows you to do this

 

[Rokku]

check my topic my tool allows you to do this

Well I'm looking for an HGSS program, not a B/W program.