Oracle SQL Assign value to variable outside BEGIN-END?

I have the following structure:

ACCEPT PVAR_FLENME PROMPT 'File Name (No Space)? '
ACCEPT PVAR_FULLROUTE PROMPT 'Full Route: '

SPOOL "&PVAR_FULLROUTE.&PVAR_FLENME.";

... which works as expected.

Now I want to make the second variable to be dependent on an Procedure without having to create it (or a Function). I would normally use COLUMN & a SELECT, but the logic within the BEGIN-END is more complex:

ACCEPT PVAR_FLENME PROMPT 'File Name (No Space)? '
DEFINE PVAR_FULLROUTE; -- I'm not sure this is valid

BEGIN
    {Series of validations}
    {How do I assign a value to PVAR_FULLROUTE from within the procedure?}
END;

SPOOL "&PVAR_FULLROUTE.&PVAR_FLENME.";

What is the correct way to assign a value to a variable from within a procedure, so I can use it in other BEGIN-END sections? Is it possible?

Here's one option.

Accept filename:

SQL> accept par_filename prompt 'Enter filename: '
Enter filename: test.txt

Create a variable whose value is then set in anonymous PL/SQL block:

SQL> var par_fullroute varchar2(20)
SQL> begin
  2    select 'this_is_route' into :par_fullroute from dual;
  3  end;
  4  /

PL/SQL procedure successfully completed.

SQL> print par_Fullroute

PAR_FULLROUTE
--------------------------------------------------------------------------------
this_is_route

OK; its value is set. Now, create a column and put bind variable (par_fullroute) into new substitution variable:

SQL> column   par_bv_route    new_value    bvr
SQL> select :par_fullroute par_bv_route from dual;

PAR_BV_ROUTE
--------------------------------------------------------------------------------
this_is_route

Everything's set; what's left is to create filename for spool:

SQL> spool "&bvr.&par_filename."
SQL> select sysdate from dual;

SYSDATE
---------
08-FEB-23

SQL> spool off;

Result: