UUID with variable length

Hi,

I have here a situation with the usage of UUID. Here the database user allows UUIDs with less then 16 byte lengths (please don't ask :-) ).

Of course there are some technical ways to do the filling of the not used bytes but I hope there is a better solution. This UUID is used
as primary Key and for indexing.

CHAR 16 is not preferred because of the risk of mistakenly changing the binary data.

Another option would be e.g. bytea but how is good would it work from a IO an latency perspective.

Or do you have some other ideas how to use a primary key datatype like UUID but with variable length?

Thanks

Dirk