Change keyboard Compose behavior

For some time I’ve been wanting to change the default behavior of my keyboard (on an Ubuntu 18.04 machine) when using the composition keys (dead-keys).
The default behavior for the double quote key (") to be a compose key, in order to be able to input charaters like ä ("+a)and ö ("+o), so if I wanted a ", I would need to press "+spacebar. I was used to just double tap the " key and get the " (from the Windows days, I think), so I wanted that, but the default is the daeresis sign (¨).

Don’t know if it’s the setup I have (a default american english keyboard with a PT-BR locale)
So my input source is: “English (US, intl., with dead keys)”
And formats are defined as: “Brasil”

After several searches and a few dead ends (ibus and ibus-tables), I finally ended up with a solution, for my use case anyway. It turns out that the compose sequences were controlled by the files in

/usr/share/X11/locale

And the file I needed to change was this one:

/usr/share/X11/locale/pt_BR.UTF-8/Compose

The files are quote self explanatory and they seem to function in a hierarchical way, with the more specialized layouts including the more generic ones and overriding where needed. The pt_BR file included the en_US one, and the values I needed overriding were in the english one. Copying the relevant section and changing the end result was easy and I just added this to the end of the file.

<dead_diaeresis> <dead_diaeresis>   : "\""   diaeresis # DIAERESIS
<Multi_key> <quotedbl> <quotedbl>   : "\""   diaeresis # DIAERESIS
<dead_acute> <dead_acute>           : "'"   acute # ACUTE ACCENT
<Multi_key> <apostrophe> <apostrophe>   : "'"   acute # ACUTE ACCENT

As I could not find an easy way to reload this, restarting the X server solved the rest.