A replacement properties.dtml and a pair of methods which cause property types to be displayed and allow them to be changed.

1. Backup your Zope dir/lib/python/OFS/properties.dtml
2. Download all three parts.
3. Replace Zope dir/lib/python/OFS/properties.dtml
4. Import the two .zexp files into your root folder

All of your standard property sheets should now have property-type dropdown lists next to each deletable property. If you check the checkboxes next to one one more properties, change their type dropdown, and then push "Change Types", you will be given a form in which you can fine-tune the values of the properties using fields appropriate to their new types.

properties.dtml is ZPLed, and the two methods are public domain.