Synonym modelling and trailing modifiers

Hi,
I am trying to copy the synonyms of a Term from an ontology to a new ontology, but part of the information (trailing modifiers) is not coded when pronto models the synonyms. The trailing modifiers are date and language. Here is an example.
Synonym structure in the original OBO file:
`synonym: "SYNONYM_1" NARROW SYN [ABC] {lang="en", date="2020-09-04"}`
The synonym printed:
`Synonym(‘SYNONYM_1’, scope='NARROW', type=SynonymType('SYN', 'SYN'), xrefs={Xref(' ABC ')})`
The result after copying the synonym in a new ontology:
`synonym: "SYNONYM_1" NARROW SYN [ABC]`
How could I add the trailing modifiers to the synonym?
Thank you,
José Luis