Hello, new here
I am writing a novel where a character calls his love "a chuisle". If she was to get a necklace with this endearment on it would it be mo chuisle or a chuisle? I understand the vocative use of a vs mo when he's addressing her, but if you're "bottling up" the endearment would it be verbatim with "a"? Thank you in advance!

Both is possible. "a chuisle" as kind of a direct speech citate.

Btw: a chuisle is vocative tense (lit. "o (my) pulse!")
But the same form also means "his pulse", because the little word "a" means a lot of things.