How do you mod maps for halo on PC?
Yes. There are a lot of mods for Halo and Halo Trail on PC.
There is no Halo 3 mod for Halo Trial. Halo Trial is one of the hardest versions of Halo to mod. There are however, custom maps for Halo Custom Edition. To get Halo Custom Edition, you need to have Halo: Combat Evolved installed on your PC, you also need your CD key. You can download Halo: Custom Edition free.