sorta back on topic, but I think I've got themes figured out. I just installed the dragon quest heroes metal slime edition theme. the unlock pkg is the same as for free dlc. or rather, the process is the same. I was having difficulty with it at first. originally, the theme stayed locked, then it completely disappeared. I'm assuming that it's like the vita with theme components being recorded in the app.db. anyway, it wasn't working for some reason. after I restarted the system, the theme and unlock pkgs worked without issue, so I'm not really sure what the problem was. it took multiple attempts, and I think the unlocker and the theme were overwriting each other, but I'm not sure what could've happened with the theme disappearing. I did test it. the theme is permanent (without hen).
edit: I found out something new. apparently, if you switch to another theme while hen isn't enabled, the unlocked theme will become locked again. I assume it's recorded by the app.db, where a rebuild of the database is also likely to make the theme locked again -- if it's even read at all! it's fine as long as you have a backup of the unlocker, which is easy to make with this python script, and the original theme or don't change the theme. this is based on my knowledge about the vita. whether it's changing the default icons manually or even using a theme, I think in both instances they're reverted back when you rebuild the database or restore the system.