How to 'add' a new key to the keyboard?

I don’t know if this is possible to do in Plasma:
I’d like to add a new symbol (í) to my keyboard when double pressing y.

Background: I bought a Czech keyboard (don’t ask why lol) but would like to use it with a Hungarian layout. It’s missing the í key when using the Hungarian layout. It does have a key combination to type í (shift+ 9), but that doesn’t work with this layout set.