To clarify the above hint:
"...the class entry of class or the function entry of function is immutable"
Neither PHP class or function definitions have any "immutable" keyword - so this note is confusing, as it implies that a PHP programmer has any control over this. In reality, the "immutable" state mentioned is an internally-controlled optimization/shared memory feature of OPcache.
Consequently, if one has a need to set (alter) the flags of a PHP class or function by means of "uopz_flags()", then it is necessary to EXCLUDE the PHP script of the referenced class or function from OPcache, using the "opcache.blacklist_filename" INI parameter.