There are a few things you can change if you like. At the beginning of each library file are some configuration variables.
You can change what character will identify the template tags (default is '=') and how many of this characters to use (default is 2 – '=='). In the same way you can change how comments will look like (default: 2x '#' – '##').
Now you can configure more. See the library code (simpleht.php/.asp) and you'll see the configuration right in the beginning of the file. You can set all those characters identifying each type of the template variables. It should work with any characteres but if it would for some reason stop working, try using chars that has no spacial meaning in regular expressions.
If you for some reason want to change the whole look of the variable and loop tags, you can go into the code and change the regular expressions that are used to look up the tags in the template. You should know what you are doing and be careful. You will not damage your data or something but the engine can stop working or behave weirdly.