hi,
you can do this by exporting Appointment entity.. in form XML
<section name="scheduling information" showlabel="true" showbar="true" locklevel="1" id="{4F40F21E-AB16-446f-9EFD-BD3F3FAAB634}" IsUserDefined="0" layout="varwidth" columns="11">
Change locklevel from '1' to '0' i.e.
<section name="scheduling information" showlabel="true" showbar="true" locklevel="0" id="{4F40F21E-AB16-446f-9EFD-BD3F3FAAB634}" IsUserDefined="0" layout="varwidth" columns="11">
to remove locked field remove it directly from form XML.i.e cell tag of that attribute.
and import it again. by changes locklevel now you are able to edit fields of "scheduling information" section.
if you find it helpfull please mark it as answer.
Pooja