None of the accessory power sockets are connected when the key is off, so they aren't suitable for connecting an external battery charger/maintainer.
You can hack the factory protection by installing a jumper wire in place of an existing protection relay. Your Owner's Manual lists the relays, one for each of the power sockets. Identify which you want to hack, make sure key is on OFF position, remove the protecting fuse specific for that relay/circuit/socket, carefully extract the relay using non-metallic tools, and place a 12ga jumper with spade terminals between pins 1 and 2 in its place. Restore the fuse. Choose which socket you want to use carefully, as stuff plugged in there will be on all the time and can/will run the battery down with the protection relay bypassed. The relays and fuses are in the Auxilliary Underhood Fuse/Relay Box.
I currently use a CTEK maintainer that uses a socket and pigtail connection right at the battery. The hood needs to be opened to access the connector, and I leave the hood "cracked" open a little with the cable passing in, so it's easy to notice. CTEK offers an extension cable that could be routed easily to the area at the base of the windscreen if leaving the hood cracked open for the cable isn't a good option. All the cars in the garage have maintainers on them now, since we just aren't driving much at all these days.
On a previous car that sat a lot near a winter ski home, I used a compact Schumacher maintainer and passed the short AC cord to the grill, along with the cord for a block heater in winter. The maintainer itself attached to the side of the battery and helped keep it warm in the non-heated mountain airport hanger where the car spent most of its life.
Yeah, possible, but the operative question is "why didn't the people who designed this thing make it much easier to use by having it plug into a 12v accessory port (aka, cigarette lighter)?"
The answer is that the wiring behind the accessory ports is fine for charging phones, running small inverters, or other light, intermittent loads. It is at best marginal for continuous use by a charger that might output more than you expect. The downside of getting it wrong is igniting your vehicle. This leaves aside issues like figuring out if variable low voltage might negatively affect any of the other electronic components this approach might power up.
There are safer ways to make your life easier. Dr. Bob's post about routing a connector to the grille is what I would try.
I've been using a Deltran Battery Tender Junior pretty much 24/7 for 2 years now on another vehicle. It does a great job. Avoid the cheap products that can cook your battery.
I'm usually pretty conservative when it comes to stuff like this.
The convenience outlets are electrically connected right to the battery primary cabling, each via a dedicated fuse and the relay, so connecting a charger to an outlet won't expose delicate electronics any more than it would connecting the same charger directly to the battery. If the OP has a concern that the connector isn't up to its continuous rating (15A), it's easy to install a smaller fuse in place of the 15A that's there from the factory. The CTEK maintainer I use has a 7.5A fuse in the pigtail, max 7 amp charge current rating, and the cigarette-lighter plug adapter from them has the same 7.5A fuse protection. Most common maintainers have a lot less current capability.
I looked hard at a couple of these options for the Pilot. One is installing a dedicated charge port that snaps into the dash at an unused switch opening by the drivers's left knee. Cable would come in through the driver's door or window. The other was installing the same snap-in port after making a similar opening in the cover by the trailer wiring connection in the left rear cargo area. Buy a spare cover now to modify, and keep the original available to restore later if needed. Then add the fuse-and-relay jumper go the trailer charging circuit to keep it connected full time, and the dedicated charge port doesn't interfere at all with the accessibility or operation of the other convenience power ports. I could even adapt the trailer connections and have the charger connections completely outside the car. Use a Molex or similar connector at the trailer port and it would break away with no damage if the car gets driven away with it still attached.
Simple option for what you want to do. Buy the charger like pictured. When you get it and unbox it throw that damn cigarette lighter plug in a drawer and forget it. Now comes the easy part.
Take the item I have marked as #1 and attach it to the battery terminals, red to positive and black to negative. Secure them nice an tight under the bolts.
Next, run the wire to the front grill area. If this one is too short, go to any good auto supply store and get one with a longer feed. This is a Schumacher style plugs so they should be interchangeable. Safely run the cable to the front grill. Find a nice place to tuck it away in the perimeter of the grill and zip tie the cable to the grill. Leave enough slack to tuck the plugin, back inside the grill so it doesn't rattle or show. Make sure the attached cap is tightly closing off the end. That's what it is there for.
When you feel you need to plug it in pull the cap off, plug in the charger cable, the cable connectors will not let you screw it up, and plug in the charger. No fuss, no muss, no opening the hood. Just remember to unplug it before you drive off, otherwise you will look like the little ole' grandma that forgot to take the gas nozzle out of the tank as you drive down the street.
Save #2 for other uses, such as a garden tractor battery in the off season etc.
If you want to get really fancy you could even get something like this and mount it in the grill/bumper area.