Well, at least one of the approaches is incorrect. I uncommented the warnings, turned them into prints and added the following to your program:

dosubstr;
print "---\n";
doregex;
[download]

Running your program gives me:

A12345 RELEASE 
  
A1 2345RELEASEA12345 
FTOP DD_BUIL+ 
  
FT OPDD_REKL+FTOP 
FTOP DD_PLAN+ 
  
FT OPDD_REKL+FTOP 
---
[download]

Abigail