Is it possible to activate specific glyph replacement between two specified characters?

Is it possible to have a specific opentype effect applied only when applicable text is set between a specific set of characters?

In other words, to have a character replacement occur for all applicable characters inside the text written between the characters specified as the start and end point.

Example 1: All numbers inside [ ] are replaced by turned variants.
Example 2: All text within { } use specified .locl forms instead of the default ones.

No, this is not possible. Generally, such effects are applied using higher-level software like CSS on the Web or Text Styles in word processors like Word or layout apps like InDesign.

You can do so to some extend. If you have only a few letters between the brackets or braces, you can add some contextual substitutions.

I see, thanks.