This can be an ugly "hack" without proper tools.
For my use, looks don't matter too much.
Of course, the warranty is lost, water can get in (only for indoor use) and it might not look so nice.

Device: https://mikrotik.com/product/RBwAPG-5HacT2HnD
Room temperature: ~25 degrees Celsius
Device temperature sensor stock: ~63 degrees Celsius (after several hours of usage) Device temperature sensor with "hack": ~53 degrees Celsius (after several hours of usage) The unit's case lacks any holes for the air to enter or exit.
Taking out the board from the case, it cannot be held by hand because of very high temperature.
I do not have an IR thermometer to be sure, but my hand tells me the board is hotter than what the sensors reports.

So I decided to test on one unit.
I cut a hole on each side of the unit to allow air convection. The unit is mounted horizontally on the wall. I know the cut looks ugly, but this was just a proof of concept. I will use a router to cut the hole.
10 degrees for just two holes is a win in my book and can make a difference in hotter ambient locations, where 10 degrees more might result in a lower performance then expected or even a non functioning device.

Maybe I should share my own hack - remove whole cover and temperature will be reduced even more! (what a surprise, right? )

The surprise would be if you could still attach the unit to a wall without the case. This is not a desk unit.
As for the little holes, that was the 1st thing I tried. Barely noticeable temperature wise.