since you need to use SAS, I assume there is more to this than stated. It appears possible to do what you need in any editor ~ notepad upward.
Perhaps you can explain.
Since the enquiry seems unrelated to this (and the other SAS) forums, you may find the most effective answer will come from addressing the fuller form of your question to your SAS Customer Support service.
This is not an ODS or Base Reporting proc question. You'll need the DATA step, INFILE and FILE statements, conditional logic, the INPUT statement, the PUT statement, and possibly the Macro facility (if you mean to use Macro variables) for your placeholder substitution.
You can downsize your program using the automatic _INFILE_ variable that contains the line that is being read from the external file once the INPUT statement is executed.
So everything can be done into a single Data step, without writing into a SAS dataset :
data _NULL_ ;
* LOAD IN HTML TEMPLATE */
infile 'C:\Folder\File.htm' LINESIZE=32000 TRUNCOVER ;
/* REPLACE TEXT */
rx=rxparse("'[_Fullname_]' to '&Fullname'") ;
call rxchange(rx,1,_infile_,_infile_) ;
/* EXPORT */
file "C:\Folder\Output.htm" ;
put _infile_ ;
As well as being prettier and shorter to write, this will same you time if your input file is long.