Using tilde character in a glyph name

Glyphs
1

Hi!
I have a following issue. My client wants a stylistic set, but the software he operates doesn’t use OpenType. He created a system where the initial alternate is named like this ~A, ~B, ~C etc.
Glyphs doesn’t let me use tilde. Even after enabling custom naming, or changing a production name on the export, this is not working. Is there a way around it? Thanks!

Kaja

2

This is an illegal name according to the Adobe glyph list specification:

All glyph names (…) require that they be entirely composed of characters from the following set: A–Z, a–z, 0–9, ‘.’ (period; U+002E FULL STOP), and ‘_’ (underscore; U+005F LOW LINE).

3

How is the tilde used in the final font? How does the system work?