Willy,
Yes, you can edit macros. It depends whether it is an embedded macro or a
saved macro. If it's a saved macro, right-click the name of the macro in
the Navigation Pane, and select Design from the popup menu. If it's an
embedded macro, then put your cursor in the property sheet for the property
the macro is embedded to, and click the little ellipsis (...) button to the
right. In both cases you end up in the macro editor window.
Having said that, I can't quite relate this to your original statement about
using a form to get criteria for a query. How is a macro involved in this?