Recently, I was working on Change Form wherein I had to save the form if the user where to choose Yes in a select box and the form was modified. But the form modification would involve even the select box change. So there were two choices, one was to reset the value of the select box to original value and then check for g_form.modified which would be true only if any other field was modified. Alternatively, you can use the below script in your onChange function. The FIELDNAME would ideally be the name of the field and that typically is tablename.fieldName.

Using the below script you can skip the form modification feature for this field alone. Hope it help and any other suggestions are welcome.

g_form.fieldChanged("FIELDNAME", false);