Can the wtpart end item field be set to no?

Two things - Is this end item primary end item for a product.  If it is, you have to remove this item from there. Also ensure that the item is not linked to any changes as an affected products.

Once the item is cleared from the above two, it will allow you to edit the end item field.

Regards

Binesh Kumar

Medtronic - MITG

Another item you can try (but in a test system first with adequate end user testing):

Locate this WTPart in the WTPARTMASTER DB table and switch the "enditem" flag from 1 to 0.

I have not specifically tried this before and there is always at least some minimal risk in DB editing, but I bet this would work too in the event that this WTPart already has links to items.