As far as input methods go, I like the Xperia Keyboard from Sony best.
However, I would like to slightly modify the English keymap. Specifically, I want to add some additional accented characters to the list of long-press alternatives for both "e" and "a".
I don't mind whether I replace some of the existing ones (so that "e" still has five accented alternatives and "a" still has seven) or add new ones; whichever is easier.
Is there any sensible way to do this?
Xperia Keyboard supports many languages which can be downloaded from its Input Method settings, and I presume some of these have several keyboard layouts (as there is an option to choose keyboard layout for your chosen language; I'm not sure as English (UK) only has one keyboard layout (QWERTY) but this option wouldn't make sense if at least some languages didn't have multiple layout options). This suggests that there is a place somewhere on my phone where I should be able to put an input language / keyboard layout file in some format and this would be recognised as one of my keyboard options in Xperia Keyboard settings.
My concern is that this may be in some part which is only accessible by if the device is rooted. I would happily root mine but to my best knowledge there is no known method to root it currently (Sony E2303, Marshmallow 6.0.1, bootloader unlock not allowed).