[anttihaapala]

I've wanted this too.

Postgres allows one to write custom data types in C or other system programming language. The only limitation is that the "type modifier", in this case the prefix, would need to fit in a "single non-negative integer", so in priciple using e.g. 5 bits per character you could get up to 6 lowercase letters, `-`, `_` etc into the prefix. Of course a custom extension would have limited utility if it doesn't land into cloud services like AWS RDS.