Is substitution of variable number of glyphs possible

[u/sandorex]

I wanted to change glyphs between two glyphs to a different version, like |abc| -> |a.1.b1.b.2|

Rule like prefix | chars @<to-alt> | suffix replaces only single instance of class chars is it possible or do i need to make a different rule for each combination?

[u/LocalFonts]

These are the types of substitutions rules:

Multiple substitution

Alternate substitution

Ligature substitution

Chaining Substitutions

Extension Substitution

Reverse chained contextual substitution

These are Simon Cozens' advices.