I'm not that familiar with the internals of the resource pack system, but try calling IReloadableResourceManager#reloadResources with a List containing your IResourcePack. The Minecraft#mcResourceManager field contains Minecraft's IReloadableResourceManager instance.
Please don't PM me to ask for help or to join your mod development team. Asking your question in a public thread preserves it for people who are having the same problem in the future. I'm not interested in developing mods with people.