Customize Long-press Symbols

It would be very nice if there were a way to adjust what symbol(s) are in the long-press menu of each key, as well as which one of those is the default. For instance:
* I use tilde (~) a lot, to indicate a sentence spoken with a joking tone. I'd gladly give up, say, double-quote on 'C' to get quicker access to it. (Yes, I know that if you turn on the dedicated number row, 'E' gets tilde as its long-press instead of 3, but that costs valuable screen real-estate.)
* The number keys,  when you have the dedicated number row on, don't have any long-press symbols assigned at all.
* As I Canadian, I use the English (UK) locale, since there isn't a dedicated Canadian English locale and we mostly use the British spellings for words. However, this means SwiftKey insists on making the default long-press symbol on 'X' the pound symbol; since our currency is the Canadian dollar, I'd much rather have it default to the dollar sign.
* As an English-speaker living in Québec, I occasionally need to type a French word or place name which contains an accented character. However the only accents which are used with any frequency are the acute, grave, and circumflex on a vowel or cedilla on 'C'; the other fifty-or-so accented characters available when the 'Show all accented characters' option is on are or little use to me.