No, because internally a thing called "Regular Expression" is used to detect chords and that thing breaks very easily. So allowing to extend it with user defined input is not possible.
But I have something else implemented last minute for the final version 3.7: If you start a line with the character
` the rest of the line will be displayed as a chord no matter what you write. Only downside: this works on whole lines. You can not use it within a chord tag.