Bash: How to create "custom identifiers"

This is an issue that will really simplify a lot of my code if it is possible.
Defining Base16 in Bash is very vague and I cannot figure how bash does it for e.g. indices.

I want to declare e.g. hex numbers as an identifier for use in indices.

As an example.
How do I declare 1A as an identifier ?

What I tried so far was to first void an make A readonly with

unset A
declare -i A
readonly A

Atfter this A can be used as an index , no problem!

But now I want to similarly set 1A as an identifier and nothing works

How is a custom identifier created in bash ?
Please use 1A as example.

(*Note: I dont mean using Posix hex identifiers such as 0xFF etc. That of course works as indices, I am talking about creating a new identifier that is 00 1A 1B etc till FF. *)

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