There is a tremendous little program called “OpenType Feature Freezer” available at https://twardoch.github.io/fonttools-opentype-feature-freezer/ which I’ve used to get around this exact problem. My first solution was to create my custom “SC” versions of typefaces by copying glyphs around in FontForge, but after engraving a piece with a French title, I realized there were going to be glyphs I’d miss, like letters with diacritical marks, or things I didn’t even know a typeface might include, like custom dashes or dollar signs. OTFF gets them all. It even has automatic re-naming functions built in, though I could never get that to work the way I wanted, so I still do the TrueType and PostScript naming manually, in FontForge. But I can’t recommend OTFF highly enough.
Anybody get really picky and also seek out petite-caps alternates as well as small-caps? That’s something I’d love to see every designer include. Ah well — someday!