Mods for 1.7.10 generally had to be rewritten for 1.8, in some cases almost from scratch, due to how different 1.8 is from 1.7.10. Converting a mod for 1.8 to 1.7.10 is likely to be similarly difficult. What mod did you want to do this for? There might already be a 1.7.10 version of it, or a reasonable substitute that is available for 1.7.10.
I wanted to do this for the CustomNPCs mod, as flying npcs where added in 1.8 but 1.7.10 hasn't been updated for 8 months. There is a 1.7.10 version but it doesn't have the flying capabilities that I wanted to use for a world I am creating.