Changing Legendary encounters

[vyvernn]

Hey guys sorry for the noobish question but im making a hack for Pokemon white where i want to change the legendary encounters, i'm making a hack with all my favourite pokemon in it which i want to change some of the legendaries for (as i was never keen on any of the horses or on the Genies either) i basically want to change a few, so in the end i want the 3 Legendary birds plus Lugia (i'm thinking of replacing the horses for them) Darkrai and Cressilia (im thinking the two available Genies) but i also want Entei, Raikou, Suicune and Giritina in there, any ideas how i would approach this, thanks in advance!!