Pillars of Eternity does a great job of emulating old-school Infinity Engine RPGs, but that hasn't stopped one modder from taking it a step further. The Pillars of Eternity IE mod adds some tweaks and changes to increase PoE's throwback feel and give you a few more UI options, as well as an assortment of other tweaks.
First and foremost, the mod lets you completely reshape the game's interface. Drag things around onscreen, change their placement, and even their size. Want your character portraits at the top of the screen? Or vertically along the side? Ability toggles, the info boxes, and everything else on your hud can be rearranged until you've got things the way you like them.
There are also some gameplay tweaks, such as the optional disabling of engagement. Engagement means that if one of the participants in melee combat tries to break away to reposition, they leave themselves prone to a free attack from their enemy. The modder feels this makes combat less tactical and more static, since once you're in melee you're less likely to uproot yourself. If you disagree and like engagement the way it is, no worries: this feature is optional and you don't have to use it.
To more closely emulate an Infinity Engine game, you can also choose to play with an option that will only allow a single tooltip to appear when you hold the Tab key, meaning you'll have to hover the mouse over anything you want to examine. Again, you don't have to enable this if you like viewing all the popups at once.
There are also some tweaks to the circles that appear around the feet of characters, both in your choice of color (it can be made blue to signify neutral NPCS) and their thickness. There's also a change to auto-saves, which will now save your game before you transition to a new area instead of after. And, you can now run while scouting, as opposed to slowly slinking, and you can loot during combat instead of having to wait for all your enemies to be dead.
All of the above changes are optional (activate them by checking their boxes on the mod menu). The IE mod also adds console commands that modders (or cheaters) will enjoy. You can get the details of these commands, a download link, and instructions on the mod's page, and the mod also has an entry on nexusmods.com.
Keep in mind, updates to Pillars of Eternity have been landing regularly as bugs are patched, and these updates tend to break mods. Always make sure the mod is compatible with the version you're playing.