Read and Write Custom of a Block using autolisp

[22352065NTPYQ]

What is the autolisp syntax to read and write Custom of a block . It can be seen by selecting the object and executing command "PR (PROPERTIES)"  through UI.
I am using Autocad electrical 2025.

[rhesusminus]

You should ask about this in the Autolisp forums: Visual LISP, AutoLISP, General Customization Forum Autodesk