The blocked sender list stored in the UAF.BBS file is a binary record. We use TIO to store the record -- "Tagged IO" -- because it's the best way to do it. There are TPL functions for reading and writing TIO records. Armed with the following information, and sufficient expertise, you can use TPL to manage the blocked sender list if you wish. Bear in mind that we are always available at a reasonable consulting rate to help you do TPL programming.
The blocked sender list is actually a nested tio record. The outermost level contains binary tio subrecords (which are read into string variables in TPL). There is one such subrecord for each blocked sender. These subrecords have tio labels 10, 11, 12, and so on. A person with 1 blocked sender has a single subrecord with label 10; if there are 2, you will find 10 and 11. So, to get the blocked sender subrecords just keep extracting tio subrecords with TIOGETS until TIOGETS indicates the subrecord was not found.
Now for the TIO format of each subrecord for a specific blocked sender. There are only two fields in each one: label 10 is a string field containing the address to block. Label 11 is an integer field indicating whether to send a bounce message to the bouncee (1=yes, 0=no).
A reasonable way to manipulate the set of subrecords in TPL would be to declare some maximum number of blocked addresses -- say, 20 -- and declare an array of strings to hold the subrecords.