LG's phones have long been popular with people who want to play with mods, and now that can begin in earnest with the LG G5. This device now has an official build of TWRP ready for flashing. With a custom recovery, you can do all sorts of neat stuff.
A custom recovery is the first step in installing mods and ROMs. You'll need an unlocked bootloader to install TWRP, but most versions of the G5 can be unlocked. The only ones with official TWRP builds so far are the T-Mobile (H830) and international (H850) variants. Both are v18.104.22.168.
Once you install TWRP, you can flash anything you want. That, of course, means that you can break things. Use your best judgement.