In that case I would recommend you go through the file I mentioned above and dig through the code there. globalSearch.jsfrag should be used to customize the global search.
Whereas, to cutomize the search page would be a little more effort. One has to have the following considerations :
1. Should the search be restiricted based on number of characters only for the keyword filed ? or would you need similar restiriction on all the attributes ?
2. Would you want a similar restiriction in case of newly introduced IBA's ?
The rendering for the navigator search page happens from <WT_HOME>\codebase\netmarkets\jsp\searchcommonSearch.jsp.
-Malavika