I am playing the Lotr mod in 1.7.10 with a few other mods including biomes o plenty. I want to start a new world where I begin in middle earth and eventually travel to the overworld however I want the biomes from biomes o plenty to be present in that overworld. is there any way to do this as when creating the world one has to select biomes o plenty to generate the respective biomes?
No unfortunately. You could just start in the overworld with biomes o plenty and then either spawn in a Ring Portal or edit your playerdata to get you to Middle-earth.