Merging into another font?

I'm trying to merge [wavefont](https://github.com/dy/wavefont) with Adobe blank, aiming to make all chars fall back to blanks if not found in visible ranges. Right now it's done via CSS fallback technique as `font-family: wavefont, blank;`.

The `mergefont wavefont.full.otf wavefont.otf AdobeBlank2VF.otf` command corrupts the font, as described here (following https://github.com/adobe-type-tools/afdko/issues/1573).

I tried patching tables via `sfntedit -a cmap=cmap-13.bin wavefont.otf` , as it is used here, but it doesn't work as needed.

I am wondering how did you generate the binares for the table patches and if that's possible to regenerate them somehow.

I also would like to ask for your opinion on if that's generally correct to take Adobe Blank as source for modifications and in what way would you implement last-resort technique in non-blank font?

Thanks!