Postgresql: type_modifier in UDT

Question

In the manual for creating UDTs in postgresql I found the following statement:

PostgreSQL allows user-defined types to take one or more simple constants or identifiers as modifiers. However, this information must be capable of being packed into a single non-negative integer value for storage in the system catalogs.

So is there really no way, to store more information that would fit in a non-negative integer? I would like e.g. to be able to store the name of a function that should be called as a default upon insertion on the data (since there might be multiple functions that could work on that data). That is not possible?