if i understand you correctly, you have a number of fields that will show up in the search and view forms, but you only want one of the fields to be able to be modified, right?
if this is the case, the easiest way to do this would be to create a "new" modify form which will only have the field shown that can be modified. you can do this by copying the record view forms and just deleting the fields that you don't want to show up in the modify form, and then renaming it to say html_default_mod_form, or whatever you want to call it. then go to the sub html_modify_form_record and look for this line:
|; &html_record_form (%rec); print qq|
and change it to:
|; &html_default_mod_form (%rec); print qq|
or whatever you renamed the new sub to. there are probably other ways to do this, but this is the method i used and it is working fine. hope this helped!
chuck