In terms of actually amending the onboard kindle keyboard AFAIK there is little that can be done. So with reference to editing the built-in keyboard - given the (now seemingly pointless) Amazon obfuscation war I think we can list this as "deeply unlikely".
When invoking it ourselves "as an overlay" to our homebrew apps there is some degree of control.
Not to retype Eureka's work the full details of invocation are here:
https://www.mobileread.com/forums/sho...8&postcount=28
I looked around for a few replacements actually recently... nothing "incredible" has reared it's head... should you find something AWESOME to port in the swanky OSK line.... I am all ears.