oct0xor has just released PS4 Registry Editor, a tool that lets you edit some registry files on the PS4. For now, the tool lets you edit existing entries in the following files: system.dat, system.idx, system.eap, system.rec. Currently, the developer says, PS4 Registry Editor does not let you add new entries as it does not support rebuilding the registry. This might come later.
download https://github.com/oct0xor/ps4_registry_editor