Question

Pega UDF to write directly to BLOB
There are some Pega UDF (pr_read_from_stream,pr_read_int_from_stream etc.) present to read directly from BLOB. Is any UDF present to write directly to BLOB without affecting the column value?
To explain it more elaborately - say we have a column col1 having value 'x' in it. We want to update col1 in pzpvstream with value 'y' without changing the column col1 value.
Is there any UDF present to do this? Or is there any other way to do this?
Thanks!