Variable expressions cannot be substituted for Address expressions in commands that expect an address to be supplied. For example, 'BREAK variable-expression' does not evaluate the variable-expression as an address. However, an IDF macro can be written that uses EXTRACT VLOC to determine the address of a variable which is then used as an operand on any IDF command:

/* REXX Variable Breakpoint                         */
/* Supply the variable name to be set breakpoint at */
ARG vbn
  IF vbn ¬= '' THEN DO
    'EXTRACT VLOC ' vbn
    IF LSM.0 = 1 THEN DO
      PARSE VAR LSM.1 . varaddr .
      'BREAK 'varaddr
    END
  END