Gboard: Set Custom Unicode Characters on Longpress or Add Custom Keyboard Keys or Layout On Gboard, when I long-press the "a" character, for example, I can see some other "a" characters pop up which have different marks or diacritics on them. By using long-press, I am able to easily type the ā and Ā characters, but we don't have such an option for "h" character for instance, as I would like to similarly type the ḥ and Ḥ characters. And similarly, I would like to be able to type some other Unicode characters like ʿ by long-pressing the ' key. These characters are accepted in standard academic Arabic romanizations and copy-pasting these Unicode characters from other applications is very inconvenient.


Is it possible to be able to add my own characters to the long-press of the current characters on Gboard? 
Or is it possible to create my own keyboard layout and add that to Gboard (like we add new languages and each language has its own key-set)?
If not, is there a way to hack-edit the language source file (when we download a language in Gboard) and assign my custom keys to them, so that when that language is set in the Gboard, it has my custom keys set in it?
Or if it is not possible on Gboard, then is there any other keyboard app that allows us to customize its keys like this?
If it is not possible on Gboard, how to suggest a custom-long-press-key-setting feature to the Gboard team?


Thanks.
For the time being, I found an alternative solution. It's not the solution that I wanted, but it does the job reasonably well. I'm posting it here so it may benefit someone else as well.

Gboard allows you to store a Personal Dictionary for each language that one installs (Gboard > Dictionary > Personal dictionary > English (US)). So in the keyboard in which you want to add some extra Unicode characters, add them in the Personal Dictionary of that language. With each item you add to the dictionary, you can also define a shortcut to it. So one can add ḥ — or whatever Unicode characters one needs easy access to — to one's personal dictionary and assign it a shortcut, for instance, I've assigned h key to ḥ. So whenever I press the h key on Gboard, ḥ appears in the suggestions above. 

It's not as consistent and elegant as adding ḥ to h's long-press, nevertheless, ḥ has now become much more easily accessible. The downside to this approach is that only one shortcut character can be assigned in this way to the h key, unlike the long-press option. But if you have a limited number of characters you wish to add easy access to in your Gboard, then this is an option. Though you could add other characters to a different combination of keys, like h1, h2, hdb, and so on.