If you enable PHP on your host, it really is extremely simple to do what you are saying.
All you need is an include file with the links defined as constants.
For example, if you want to reference index.htm then think of a name to call it, home say, then create a text file called something like "links.inc" and define home as a constant who's value is index.htm
Just add more lines for more constants.
Then in your html pages you then place the line
<?php include(links.inc) ?>
And in each html file you replace each link with the appropriate constant..
<?php echo home; ?>