Custom Parameter to replace feature

I’m trying to replace a feature in an exported instance with custom parameters like this:

The original feature is removed but the new one is not getting into the font. Am I doing this right?

This looks OK. And it works with a small test font. So could you send me our file, that I can have a look?

I switched to replacing a prefix instead and understood how this works. I guess the replace feature would have worked equally well. This is an extremely useful feature. I use this to make multiple versions of my font with the same glyphs but different sets of features.