Hello.
In that case what you are looking for is a special keyboard for the language, and this can be done with Keyman. You can search if there is a keyboard for your language on keyman.com, or get help to build one using Keyman Developer.
Having this you will be able to use the Paratext keyboard configuration and have, for example, your keyboard created in Keyman work for the text and your English keyboard for notes.
If your need is to change few characters I am of the same opinion as Phil, that Autocorrect.txt would be enough just by better adjusting the combination.
In the case of Autocorrect.txt, it is good to note that this is not its function, so it will not satisfy this request. The purpose of Autocorrect.txt is to apply to all places in the project. This is useful, for example, when the team wants to use long dashes or leading quotation marks, which cannot be achieved directly with a physical keyboard.
Saludos,
Pepe.